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Ten-codes, officially known as ten signals, are brevity codes used to represent common phrases in voice communication, particularly by US public safety officials and in citizens band (CB) radio transmissions. The police version of ten-codes is officially known as the APCO Project 14 Aural Brevity Code.[1]

The codes, developed during 1937–1940 and expanded in 1974 by the Association of Public-Safety Communications Officials-International (APCO), allow brevity and standardization of message traffic. They have historically been widely used by law enforcement officers in North America, but in 2006, due to the lack of standardization, the U.S. federal government recommended they be discontinued in favor of everyday language.[2]

History

[edit]

APCO first proposed Morse code brevity codes in the June 1935 issue of The APCO Bulletin, which were adapted from the procedure symbols of the U.S. Navy, though these procedures were for communications in Morse code, not voice.[3]

In August 1935, the APCO Bulletin published a recommendation that the organization issue a handbook that described standard operating procedures, including:[4]

  1. A standard message form for use by all police departments.
  2. A simple code for service dispatches relating to corrections, repetitions, etc.
  3. A standard arrangement of the context of messages, (for example, name and description of missing person might be transmitted as follows: Name, age, height, weight, physical characteristics, clothing; if car used, the license, make, description and motor number. This information would actually be transmitted in the text of the message as follows: John Brown 28-5-9-165 medium build brown eyes dark hair dark suit light hat Mich. 35 lic. W 2605 Ford S 35 blue red wheels 2345678 may go to Indiana).
  4. A standard record system for logging the operation of the station.
  5. Other important records in accordance with the uniform crime reporting system sponsored by the International Association of Chiefs of Police.

The development of the APCO Ten Signals began in 1937[5] to reduce use of speech on the radio at a time when police radio channels were limited. Credit for inventing the codes goes to Charles "Charlie" Hopper, communications director for the Illinois State Police, District 10 in Pesotum, Illinois. Hopper had been involved in radio for years and realized there was a need to abbreviate transmissions on State Police bands.[6] Experienced radio operators knew the first syllable of a transmission was frequently not understood because of quirks in early electronics technology. Radios in the 1930s were based on vacuum tubes powered by a small motor-generator called a dynamotor. The dynamotor took from 1/10 to 1/4 of a second to "spin up" to full power. Police officers were trained to push the microphone button, then pause briefly before speaking; however, sometimes they would forget to wait. Preceding each code with "ten-" gave the radio transmitter time to reach full power. An APCO Bulletin of January 1940 lists codes assigned as part of standardisation.[7]

In 1954, APCO published an article describing a proposed simplification of the code, based on an analysis conducted by the San Diego Police Department.[8] In the September 1955 issue of the APCO Bulletin, a revision of the Ten-Signals was proposed,[9] and it was later adopted.

The Ten Signals were included in APCO Project Two (1967), "Public Safety Standard Operating Procedures Manual", published as study cards in APCO Project 4 (1973), "Ten Signal Cards", and then revised in APCO Project 14 (1974).[10][11][12][13]

[edit]

Ten-codes, especially "10-4" (meaning "understood") first reached public recognition in the mid- to late-1950s through the television series Highway Patrol, with Broderick Crawford.[citation needed]

Ten-codes were adapted for use by CB radio enthusiasts. C. W. McCall's hit song "Convoy" (1975), depicting conversation among CB-communicating truckers, put phrases like "10-4" and "what's your twenty?" (10-20 for "where are you?") into common use in American English.[citation needed]

The movie Convoy (1978), loosely based on McCall's song, further entrenched ten-codes in casual conversation, as did the movie Smokey and the Bandit.

The New Zealand reality television show Ten 7 Aotearoa (formerly Police Ten 7) takes its name from the New Zealand Police ten-code 10-7, which means "Unit has arrived at job".[14][15]

Police officer retirement (North America)

[edit]

Often when an officer retires, a call to dispatch is made. The officer gives a 10-7 code (Out of service) and then a 10-42 code (ending tour of duty).[16][17]

Signals by time period (North America)

[edit]
Signal APCO Meaning
1937 APCO 1939 First Published Set (17 signals)[18] 1940 (APCO Standards Committee)[7][19] 1955 (National Operating Procedure Committee)[20] APCO Project 2 (1967)[21] APCO Project 4 (1973) APCO Project 14 (1974)[22][23] Clear Speech

(c. 1971)

(plain language to replace Ten Codes)[24]

Phrase Word Brevity Code (c. 1979)[25]
Procedure and Officer Details
10-MAX AWOL - - - Corrupt Officer Officer not following orders Insubord­ination/​Rogue Officer
Go Ahead
Under Control
In Pursuit
Traffic Stop
10-0 — — — — Use caution
10-1 Receiving poorly. Unable to copy - change location Signal Weak Unable to copy - change location Unreadable
10-2 Receiving well. Signals good Signal Good —
10-3 Stop transmitting. Disregard last information Stop transmitting Stop Transmitting
10-4 Acknowl­edgement. Message received Acknowl­edgement Affirmative (Ok) Roger Roger/​Affirmative
10-5 Relay. Relay (To) Relay
10-6 Busy. Busy, stand by Busy -Stand by unless urgent Busy Busy
10-7 Out of service. Out of service (Give location and/or telephone number) Out of Service Out at ... Out of Service
10-7 A — Not Available
10-7 B Off Radio
10-8 In service. In Service Clear In Service
10-9 Repeat, conditions bad. Repeat Say Again
10-10 Out of service—subject to call. On minor detail, subject to call Fight in progress Negative —
10-11 Dispatching too rapidly. Stay in service Dog Case ... On Duty On Radio
10-12 Officials or visitors present. Visitors or officials present Stand by (stop) Stand By (Stop) Stand by Stand By
10-13 Advise weather and road conditions. Weather and road conditions Weather and road report Existing Conditions Weather report/​road report
10-14 Convoy or escort. Convoy or escort Report of prowler Message/​Information — Prepare to Copy
10-15 We have prisoner in custody. Civil disturbance Message Delivered Disturbance
10-16 Pick up prisoner at ... Domestic trouble Reply to Message —
10-17 Pick up papers at ... Meet complainant Enroute Responding
10-17 A — — — — Theft
10-17 B Vandalism
10-17 C Shoplifting
10-18 Complete present assignment as quickly as possible. Anything for us? Complete assignment quickly Urgent Priority
10-19 Return to your station. Nothing for you Return to ... (In) Contact Return to ...
10-20 What is your location? Location Location Location Location
10-21 Call this station by telephone. Call ... by phone Call (...) by Phone Call ... Telephone
10-22 Take no further action last information. Report in person to ... Disregard Disregard
10-23 Stand by until no interference. Arrived at scene Arrived at Scene On scene
10-24 Trouble at station—unwelcome visitors—all units vicinity report at once. Finished with last assignment Assignment completed Assignment Completed — Available
10-25 Do you have contact with...? Operator or officer on duty? Report in person to (meet) ... Report to (Meet) ... Meet ... or contact ...
10-26 Can you obtain automobile registration information? Holding subject, rush reply Detaining subject, expedite Estimated Arrival Time Detaining subject, expedite
10-27 Any answer our number...? Request driver's license information Drivers license information License/​Permit Information Drivers license information on ...
10-28 Check full registration information. Request full registration information Vehicle registration information Ownership Information Registration information on ...
10-29 Check for wanted. Check record for wanted Check records for wanted. Records Check Check for wanted on ...
Emergency or Unusual
10-30 Does not conform to rules and regulations. Illegal use of radio Danger/​Caution — Use Caution
10-31 Is lie detector available? Emergency basis, all squads, 10-11 Crime in progress Pick Up —
10-31 A — — — — Burglary
10-31 B Robbery
10-31 C Homicide
10-31 D Kidnapping
10-31 E Shooting
10-32 Is drunkometer available? Chase, all squads stand by Man with gun ... Units Needed (Specify) —
10-33 Emergency traffic at this station—clear? Emergency traffic this station EMERGENCY Help Me Quick Help Officer
10-34 Clear for local dispatch? Trouble at station, assistance needed Riot Time
10-35 Confidential information. Major crime, blockade Major crime alert —Reserved—
10-36 Correct time? — Correct time
10-37 Operator on duty? No rush Investigate suspicious vehicle
10-38 Station report—satisfactory. Hurry, but do not use red light or siren Stopping suspicious vehicle (Give station complete description before stopping). Traffic stop on ...
10-39 Your Nr...delivered to addressee. Use red light and siren Urgent-Use light and siren —
General Use Private Use
10-40 Advise if Officer...available for radio call. Notification Silent run - No light or siren —
10-41 Tune to ... kcs. for test with mobile unit or emergency service. Car change at ... Beginning tour of duty
10-42 — Crew change at ... Ending tour of duty Off duty
10-43 Take school crossing Information —
10-44 — Request permission to leave patrol ... for ... Request for ...
10-45 Animal carcass in ... lane at ... —
10-46 Assist motorist Assist motorist
10-47 Emergency road repairs needed —
10-48 Traffic standard needs repairs
10-49 Hourly report mark Traffic light out East bound green light out (etc.)
Accident and Vehicle Handling
10-50 — Auto accident, property damage only Accident—F, PI, PD Traffic (F, PD)

Traffic

  • Hit and run
  • Injury
  • No injury reported
  • Unknown
  • Private property, location
10-51 Auto accident, wrecker sent Wrecker needed —
10-52 Auto accident, personal injuries, ambulance sent Ambulance needed
10-53 Auto accident, fatal Road blocked
10-54 — Livestock on highway
10-55 Drunken driver Intoxicated driver
10-56 — Intoxicated pedestrian Drunk pedestrian
10-57 — Hit and run—F, PI, PD —
10-58 Is wrecker on the way? Direct traffic
10-59 Is ambulance on the way? Convoy or escort
Net Message Handling
10-60 What is next item (message) number? What is your next message number? Squad in vicinity —
10-61 Stand by for CW traffic on ... kcs. CW traffic Personnel in area.
10-62 Unable to copy phone—use CW. Any answer our Nr. ... Reply to message
10-63 Net directed. Time Prepare to make written copy Prepare to copy
10-64 Net free. — Message for local delivery —
10-65 Clear for item (message) assignment? Clear for message assignment Net message assignment
10-66 Clear for cancellation? Clear for cancellation Message cancellation
10-67 Stations...carry this item (message). Clear for net message Clear to read net message
10-68 Repeat dispatch. — Dispatch information
10-69 Have you dispatched...? Message received
Fire
10-70 Net message (State net traffic). Fire, phone alarm Fire alarm Fire
10-71 Proceed with traffic in sequence (busy here). Box alarm Advise nature of fire (size, type, and contents of building) —
10-72 — Second alarm Report progress on fire
10-73 Third alarm Smoke report
10-74 Fourth alarm Negative Negative
10-75 Fifth alarm In contact with —
10-76 Fire equipment needed En Route En route ...
10-77 Fire, grass ETA (Estimated Time of Arrival) ETA (Estimated time of arrival)
10-78 Set up command post Need assistance Request Assistance
10-79 Report progress on fire Notify coroner Notify coroner (to be done by phone whenever possible)
The 80 series is reserved for assignment by nets for local use. Personal Favors —
10-80 ... tower lights at this station burned out. — — Chase
10-81 Officer Nr. ... will be at your station ... —
10-82 Reserve room with bath at hotel for officer Nr. ... Reserve hotel room Reserve lodging
10-83 Have officer Nr. ... call this station by telephone. — —
10-84 Advise telephone Nr. ... your city that officer Nr. ... will not return this date. If meeting ... advise ETA
10-85 Officer ... left this station for ... (Jefferson City) (Des Moines) at ... Will be late
10-86 Officer ... left this station for ... at ... —
10-87 Officer Nr. ... will be in ... if officer Nr. ... will be in. Meet the officer at ______.
10-88 What phone number shall we call to make station to station call to officer Nr. ...? Advise phone number for station to station call Advise present telephone number of ...
10-89 Request radio service man be sent to this station... Radio transmission — Bomb threat
Technical
10-90 Radio service man will be at your station .... Transmit on alternate frequency Bank alarm Alarm (type of alarm)
10-91 Prepare for inspection (date) ... (time) ... — Unnecessary use of radio Pick up prisoner
10-92 Your quality poor—transmitter apparently out of adjustment. — Parking complaint
10-93 Frequencies to be checked this date. Frequency check Blockade —
10-94 Test—no modulation—for frequency check. Give me a test Drag racing
10-95 Test intermittently with normal modulation for ... — — Prisoner in custody
10-96 Test continuously with tone modulation for ... Mental subject —
10-97 — — Check traffic signal
10-98 Prison or jail break Prison/jail break
10-99 Records indicate wanted or stolen Wanted/​stolen

Usage by Areas

[edit]

New Zealand

[edit]

The New Zealand Police use a variety of radio communication codes including its own version of 10-codes seen below.[14]

Code Meaning Activity
10-0 Off duty In use
10-1 Broadcast to all units In use
10-2 Enroute to job/event In use
10-3 Available In use
10-4 Repeat your last message In use
10-5 Out of service for a short time Not in use
10-6 Change radio channel In use
10-8 Arrived at job/event In use
10-9 Busy but Available In use
10-10 Officer requires immediate assistance (call for help) In use

Philippines

[edit]

TxtFire Philippines Fire-Specific 10-Codes

[edit]

TxtFire Philippines employs a subset of its standard 10-codes exclusively for fire-response operations. These fire-specific signals are used to dispatch and coordinate firefighting resources on VHF/UHF radio.

Fire-specific code list

[edit]
Code Meaning
10-23 Arrived at scene
10-45 Fire-service vehicle
10-70 For Verification, Fire alarm (structure)
10-71 Advise nature of fire
10-73 Request additional fire truck
10-74 Negative Fire

Fire response protocols

[edit]
  • Codes 10-70 through 10-73 automatically trigger dispatch of firefighting units and apparatus.
  • Code 10-45 is used to identify any fire-service vehicle (engine, ladder, tanker, etc.) on the air.
  • All fire-specific traffic takes priority over routine and non-fire messages on the main frequency.

Operational procedures

[edit]

Emergency protocols

[edit]

Codes 10-70 through 10-73 are designated as fire-specific codes that trigger automatic dispatch protocols within the TxtFire network.

Code 10-33 is reserved exclusively for life-threatening emergencies, requiring all non-essential radio traffic to cease immediately.

Communication guidelines

[edit]

Before initiating non-emergency communication with another station, operators must first request permission using code "10-75" from base control and complete the communication within three minutes, or transfer to a secondary channel.

During curfew hours (22:00–06:00), only emergency traffic is permitted on the main frequency; routine communications are prohibited.

Base control strictly prohibits vulgar language and commercial or personal advertisements on all frequencies.[26]

Replacement with plain language

[edit]

While ten-codes were intended to be a terse, concise, and standardized system, the proliferation of different meanings can render them useless in situations when officers from different agencies and jurisdictions need to communicate.

In the fall of 2005, responding to inter-organizational communication problems during the rescue operations after Hurricane Katrina, the United States Federal Emergency Management Agency (FEMA) discouraged the use of ten-codes and other codes due to their wide variation in meaning.[27][28] The Department of Homeland Security's SAFECOM program, established in response to communication problems experienced during the September 11 attacks also advises local agencies on how and why to transition to plain language,[29] and their use is expressly forbidden in the nationally standardized Incident Command System, as is the use of other codes.[30]

APCO International stated in 2012 that plain speech communications over public safety radio systems is preferred over the traditional 10-Codes and dispatch signals.[31] Nineteen states had changed to plain English by the end of 2009.[32] As of 2011, ten-codes remained in common use in many areas, but were increasingly being phased out in favor of plain language.[2]

Phrase Word Brevity Code

[edit]

About 1979, APCO created the Phrase Word Brevity Code as a direct replacement for the Ten-code.[25]

Phrase Word Brevity Code
Phrase word English meaning APCO Ten-code
Use Caution Caution: dangerous condition is suspected to exist. 10-0
Unreadable Radio signal is too weak to receive. 10-1
Out of Service Unit, vehicle or person is not working 10-7
In Service Unit, vehicle or person is working but not necessarily "available" or "on radio." 10-8
Available Unit is in service ready to accept assignment, not necessarily by radio. 10-24
Not Available Unit cannot accept another assignment, but may be "on radio." 10-7A
Prepare to Copy Dispatcher is about to give lengthy message. 10-14
Go You have been given clearance to transmit your message. - -
Roger (Received) Message received and understood. 10-4
Say Again (Repeat) Repeat your message. 10-9
Stand By Stop transmitting and wait for further instructions. 10-12
Disregard (Recall) Cancel your present assignment. 10-22
Off Radio Unit is not capable of being contacted by radio, but may be "available." 10-7B
On Radio Unit is capable of being contacted by radio, but not necessarily "available." 10-11
Responding Unit is en route to assigned location. 10-17
Under Control Situation is under control when no further assistance is anticipated. - -
Telephone (Tel. # or person) Call by telephone specified number or person. 10-21
Priority When transmitted, means that the following transmission must have immediate attention. - -
In Pursuit Unit is chasing a vehicle and requires assistance from other units. - -
Traffic Stop Unit is going to stop a motorist. - -
Help Officer Help me quick (emergency). 10-33
Affirmative Yes. 10-4

ICS Clear Text

[edit]

In 1980, the National Incident Management System published a document, ICS Clear Text Guide, which was another attempt to create a replacement for Ten-codes. The list of code words was republished in the 1990 Montana Mutual Aid and Common Frequencies document.[33]

ICS Clear Text Guide[33]
Procedure word Meaning
Unreadable Used when signal received is not clear. In most cases, try to add the specific trouble. Example: "Unreadable, background noise."
Loud and Clear Self-explanatory
Stop Transmitting
Copy, Copies Used to acknowledge message received. Unit radio identifier must also be used. Example: "Engine 2675, copies."
Affirmative Yes
Negative No
Respond, Responding Used during dispatch – proceed to or proceeding to an incident. Example: "Engine 5176, respond ..." or "St. Helena, Engine 1375 responding."
Enroute Normally used by administrative or staff personnel to designate destinations. Enroute is NOT a substitute for responding. Example: "Redding, Chief 2400 enroute RO II."
In-quarters, with Station Name or Number Used to indicate that a unit is in a station. Example: "Morgan Hill, Engine 4577 in-quarters, Sunol."
Uncovered Indicates a unit is not in-service, because there are no personnel to operate it.
Out-Of-Service Indicates a unit is mechanically out of service. Example: "Aburn, transport 2341, out-of-service." Note, when repairs have been completed the following phrase should be used: "Aburn transport 2341, back in-service, available."
In-Service This means that the unit is operating, not in response to a dispatch. Example: "Fortuna, Engine 1283, in-service, fire prevention inspections."
Repeat Self-explanatory
Weather
Return to Normally used by communications center to direct units that are available to a station or other location.
What is your Location? Self-explanatory
Call ____ by Phone
Disregard Last Message
Stand-By
Vehicle Registration Check
Is ____ Available for a Phone Call?
At Scene Used when Units arrive at the scene of an incident. Example: "Perris, Engine 6183, at scene."
Available at Residence Used by administrative or staff personnel to indicate they are available and on-call at their residence.
Can Handle Used with the amount of equipment needed to handle the incident. Example: "Susanville Battalion 2212, can handle with units not at scene."
Burning Operations Self-explanatory
Report on Conditions
Fire under Control
Emergency Traffic Only Radio users will confine all radio transmissions to an emergency in progress or a new incident. Radio traffic which includes status information such as responding, reports on conditions, at scene and available will not be authorized during this period.
Emergency Traffic Term used to gain control of radio frequency to report an emergency. All other radio users will refrain from using that frequency until cleared for use by the communications center.
Resume Normal Traffic Self-explanatory
[edit]
Main article: Police code

Brevity codes other than the APCO 10-code are frequently used, and include several types:

  • The California Highway Patrol uses ten-codes, along with an additional set of eleven- and higher codes.[34]
  • California Penal Code sections were in use by the Los Angeles Police Department as early as the 1940s, and these Hundred Code numbers are still used today instead of the corresponding ten-code. Generally these are given as two sets of numbers[citation needed]
  • The New York Fire Department uses its own ten-code system.[35]
  • Fire and Emergency New Zealand uses a system of "K-codes" to pass fire appliance availability statuses as well as operational messages. For example, "K1" means "proceeding to incident", "K99" means "Structure fire, well involved", and "K41" means "fatality" (a reference to the Ballantyne's fire, New Zealand's deadliest, which killed 41 people).[36][37][38] The New Zealand Police also use some K-codes,[39] with completely unrelated meanings to those used by FENZ; Police code "K1" means "no further police action required".
  • Telegraph and teletype procedures
    • Q code and prosigns for Morse code are used in amateur radio, aviation, and marine radio. They provide specific abbreviations for concepts related to aviation, shipping, RTTY, radiotelegraph, and amateur radio.[40] In radiotelegraph operation, a Q code is often shorter,[41] and provides codes standardized by meaning in all languages – essential for international shortwave radio communications.
    • Z codes are used for military radio communications NATO countries, and like Q codes are standardized across languages.

See also

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References

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[edit]
[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

Ten-code

View on Grokipedia
from Grokipedia
Ten-codes, also known as 10-codes or APCO Ten Signals, are a set of numeric brevity codes prefixed with "10" that are used primarily by law enforcement, , and fire departments to transmit routine messages concisely over radio communications. These codes enable quick exchanges of information, such as status updates or incident reports, thereby reducing airtime on busy channels and minimizing the risk of misinterpretation in high-stress environments. Common examples include 10-4 for "acknowledgment" or "," 10-20 for "," and 10-33 for "emergency traffic" requiring immediate assistance. The ten-codes originated in the early amid the advent of public safety radio technology, which was limited by single-channel systems and frequent congestion. They were formally established in 1937 as one of the earliest projects of the Association of Public-Safety Communications Officials (APCO), with significant development led by Charles "Charlie" Hopper, communications director for the Illinois State Police. Adapted from earlier naval procedure symbols, the codes were proposed by APCO in 1935 to promote standardization and efficiency in procedures. By 1940, APCO had published the first official list, which evolved over time but retained its core numeric format. Despite their widespread adoption for over eight decades, ten-codes lack a true national standard, leading to variations across jurisdictions—such as the integration of local penal codes in some departments (e.g., 187 for ). This inconsistency has caused critical communication failures during multi-agency responses, including the 1982 crash, the , 2001 attacks, and in 2005. In response, the U.S. Department of Homeland Security and the recommended in 2006 that agencies phase out ten-codes in favor of to enhance and clarity. While many departments have transitioned, others retain them due to tradition, training challenges, and concerns over officer safety, with some retaining a limited subset for specialized operations.

Origins and History

Development in Early Radio Communications

The Association of Public-Safety Communications Officials (APCO), founded in , played a pivotal role in the early development of brevity codes for radio communications amid the constraints of emerging voice technology. In the June 1935 issue of The APCO Bulletin, APCO proposed the first list of brevity signals, adapted from U.S. Navy procedure symbols and the Association of American Railroads' codes, to facilitate concise transmissions in public safety operations. These initial "ten-signals" were designed primarily for but laid the groundwork for voice adaptations as police departments transitioned from to amplitude modulation (AM) voice radio in the 1930s. A key figure in advancing these codes for practical police use was Charles "Charlie" Hopper, communications director for the Illinois State Police, who in 1937 began developing a set of numeric brevity codes to address the limitations of early systems. Hopper, a skilled operator since 1938, recognized that the single-channel AM frequencies allocated by the in 1933—often shared across entire metropolitan areas—created severe bandwidth constraints, leading to frequent interference and delays in critical dispatches. Prior to widespread capability, one-way broadcasts from dispatch to patrol cars in the late lacked acknowledgments, prompting the need for quick numeric phrases once bidirectional communication became feasible around 1933. Early ten-codes, such as 10-4 for acknowledgment ("") and 10-20 for location inquiry, directly addressed these one-way limitations by enabling rapid confirmations and status updates without lengthy verbal exchanges, thereby minimizing airtime on congested channels. APCO refined and expanded Hopper's list into the official "Ten Signals" by , promoting their adoption to standardize brevity across agencies while conserving the narrow spectrum available for voice transmissions.

Evolution and Standardization Attempts

Following , the ten-codes, initially standardized in the January 1940 APCO Bulletin as a set of brevity signals for communications, underwent expansions to accommodate increasing inter-agency coordination needs. These codes, originally designed for efficient voice transmissions amid limited radio technology, saw adaptations as public safety operations grew more complex, with agencies incorporating additional signals for scenarios like traffic control and dispatching. In the 1970s, the Association of Public-Safety Communications Officials-International (APCO) intensified efforts toward national standardization to mitigate widespread variations that hindered . APCO Project 2, completed in 1967, integrated the ten-codes into the "Public Safety Standard Operating Procedures Manual," providing a foundational framework for uniform procedures across departments. This was followed by Project 4 in 1973, which produced "Ten Signal Cards" as training aids to promote consistent radio terminology and reduce transmission errors. A pivotal advancement came with APCO Project 14 in 1974, which revised the Ten-Signal code into a recommended national standard featuring a numeric-only format prefixed by "10" for enhanced brevity and clarity. The project included a "Ten Signal Comparison" analysis documenting discrepancies among regional implementations, such as differing meanings for codes like 10-1 (signal weakness in some areas versus receiving poorly in others), underscoring the urgency for unification to improve response times and training efficiency. Despite these initiatives, full adoption remained elusive due to local preferences, leading to persistent adaptations. The codes also evolved technically across eras, with pre-1950s versions reflecting teletype-influenced brevity suited to early radio systems, while post-1950s revisions optimized them for direct voice communications, as seen in updated definitions from 1940 to 1974 that shifted emphases toward real-time operational clarity. In the 1980s, (FCC) rules on spectrum efficiency for private land mobile services indirectly bolstered the use of such brevity codes in public safety radio, emphasizing concise transmissions before broader federal recommendations in later decades favored for .

Core Ten-codes and Meanings

Standard Codes for General Emergency Use

The ten-codes standardized for general emergency use originated from efforts by the Association of Public-Safety Communications Officials-International (APCO) to streamline radio transmissions amid limited bandwidth in the , with the core framework established between and 1940 and revised in the 1974 APCO Project 14. These codes enable brief, coded exchanges between dispatchers and responders in police, , and medical services, reducing airtime while maintaining clarity during high-stress operations. Over time, the general codes have shown strong historical consistency in their primary meanings, particularly for basic acknowledgments and urgent alerts, fostering interoperability across North American agencies despite localized adaptations. For example, codes like 10-4 (acknowledgment) and 10-33 (emergency traffic) are widely upheld without alteration, while others, such as 10-50 (typically denoting a vehicle accident), may be tweaked in practice—sometimes interpreted as a request for a wrecker in widespread but non-standard usage. This balance of uniformity and flexibility has sustained their role in multi-agency responses, though the Federal Communications Commission has encouraged plain language since the 1980s to mitigate confusion from variations. While the following list reflects the primary meanings from the 1974 APCO Project 14, actual usage varies by jurisdiction. The codes are functionally categorized to cover communication status, operational movements, administrative tasks, traffic incidents, and emergencies, allowing responders to convey complex situations succinctly. Below is the core APCO list of ten-codes from 10-1 to 10-99, reflecting their primary, standardized meanings for general emergency contexts.
CodeMeaning
10-1Unable to copy—change location
10-2Signal good
10-3Stop transmitting
10-4Acknowledgment (OK)
10-5Relay
10-6Busy—stand by unless urgent
10-7Out of service
10-8In service
10-9Repeat
10-10Fight in progress
10-11Dog case
10-12Stand by (stop)
10-13Weather/road report
10-14Prowler report
10-15Civil disturbance
10-16Domestic problem
10-17Meet complainant
10-18Quickly
10-19Return to ...
10-20Location
10-21Call ... by phone
10-22Disregard
10-23Arrived at scene
10-24Assignment completed
10-25Report in person (meet) ...
10-26Detaining subject; expedite
10-27Driver's license information
10-28Vehicle registration information
10-29Check for wanted
10-30Unnecessary use of radio
10-31Crime in progress
10-32Man with gun
10-33Emergency
10-34Riot
10-35Major crime alert
10-36Correct time
10-37Suspicious vehicle
10-38Stopping suspicious vehicle
10-39Urgent—use light/siren
10-40Silent run—no light/siren
10-41Beginning tour of duty
10-42Ending tour of duty
10-43Information
10-44Permission to leave ... for ...
10-45Animal carcass at ...
10-46Assist motorist
10-47Emergency road repair at ...
10-48Traffic standard repair at ...
10-49Traffic light out at ...
10-50Accident (fatal, injury, property damage)
10-51Wrecker needed
10-52Ambulance needed
10-53Road blocked at ...
10-54Livestock on highway
10-55Intoxicated driver
10-56Intoxicated pedestrian
10-57Hit and run (fatal, injury, property damage)
10-58Direct traffic
10-59Convoy or escort
10-60Squad in vicinity
10-61Personnel in area
10-62Reply to message
10-63Prepare to make written copy
10-64Message for local delivery
10-65Net message assignment
10-66Message cancellation
10-67Clear to receive net message
10-68Dispatch information
10-69Message received
10-70Fire alarm
10-71Advise nature of fire
10-72Report progress on fire
10-73Smoke report
10-74Negative
10-75In contact with ...
10-76En route ...
10-77Estimated time of arrival (ETA)
10-78Need assistance
10-79Notify coroner
10-80Chase in progress
10-81Breathalyzer report
10-82Reserve lodging
10-83Work school crossing at ...
10-84If meeting ..., advise ETA
10-85Delayed due to ...
10-86Officer/operator on duty
10-87Pick up/distribute checks
10-88Present phone number of ...
10-89Bomb threat
10-90Bank alarm at ...
10-91Pick up prisoner/subject
10-92Improperly parked vehicle
10-93Blockade
10-94Drag racing
10-95Prisoner/subject in custody
10-96Mental subject
10-97Check (test) signal
10-98Prison/jail break
10-99Wanted/stolen indicated

Specialized Codes for Law Enforcement

In contexts, ten-codes have been adapted to address police-specific scenarios, emphasizing procedural efficiency during patrols, investigations, and tactical operations. These specialized codes facilitate rapid communication over radio channels, particularly in high-stakes situations where brevity is essential to maintain operational security and response times. Unlike general emergency codes, police variants focus on incident types common to law enforcement, such as disturbances, arrivals at scenes, and status updates for personnel. The Association of Public-Safety Communications Officials (APCO) expanded these in the 1930s and 1940s to standardize communications amid growing radio use in policing. Key police-specific ten-codes include those for handling civil disturbances and suspicious activities. For instance, 10-15 signals a civil disturbance, often used to report gatherings that could escalate into riots or public order issues, prompting coordinated responses. 10-23 indicates arrival at the scene, allowing officers to confirm their presence and initiate on-site assessments without lengthy descriptions. Similarly, 10-37 denotes a suspicious , alerting dispatch to potential threats requiring investigation. Off-duty signals, such as 10-7 for out of service, mark an officer's temporary or permanent unavailability, often used at shift ends or during breaks.
CodeMeaning in Law Enforcement ContextExample Use
10-15Civil disturbanceReporting a crowd or altercation at a public event.
10-23Arrived at sceneConfirming presence during a response to a call.
10-37Suspicious Notifying of a vehicle requiring investigation.
10-7Out of serviceIndicating end of availability, e.g., for lunch or .
Tactical applications of these codes are prominent in dynamic police operations, such as pursuits and mission closures. 10-23, meaning arrived at assignment, is frequently employed in vehicle pursuits to signal an officer's position relative to a , enabling real-time coordination among units. 10-24, denoting mission completed, confirms the resolution of an operation, such as securing a perimeter or apprehending a , allowing dispatch to assign new tasks. Related codes like 10-80 for chase in progress further support tactical brevity during high-speed engagements. Variations exist in retirement and off-duty protocols across North American agencies, reflecting local adaptations of APCO standards. While 10-7 universally signifies out of service, 10-42 specifically denotes end of shift or , often used in formal s to acknowledge an officer's career conclusion. Some departments combine these, such as issuing 10-7 followed by 10-42, to differentiate routine breaks from permanent off-duty status. Era-based shifts in ten-code usage highlight their evolution from early 20th-century foot patrols to modern vehicle-centric policing. Pre-1960s, codes like 10-23 were applied in beats for routine scene arrivals during foot patrols, emphasizing localized responses in urban areas. By the late , with the rise of motorized patrols post-World War II, tactical codes such as 10-23 and 10-80 became integral to vehicle pursuits, adapting to faster, multi-unit chases on highways and streets. This transition underscores how ten-codes evolved to match technological and operational changes in .

Variations and Regional Adaptations

North American Agency-Specific Variations

Ten-codes exhibit significant variations across North American agencies, primarily due to local adaptations for operational needs, resulting in non-standardized interpretations that complicate interoperability. For instance, the assigns 10-15 to mean "prisoner in custody," while the standard Association of Public-Safety Communications Officials (APCO) interpretation of 10-15 denotes a "civil disturbance." Similarly, 10-13 can signify "officer needs assistance" in some departments but "request wrecker" in others, highlighting how agencies modify codes to suit regional priorities. These differences stem from the lack of a universal standard, as each historically developed systems to enhance brevity and security in radio transmissions. State and provincial agencies further illustrate these inconsistencies. In , the Provincial Police uses 10-88 to request a K9 unit, whereas other agencies interpret it as "advise telephone number" or, in some cases, an urgent call for supervisor assistance. The employs a core set of ten-codes similar to APCO standards. These agency-specific modifications, while efficient internally, often arise from unique environmental demands, like high-volume traffic enforcement in or cross-border activities in . Beyond law enforcement agencies, ten-codes have been adapted for civilian use in North America, particularly in Citizens Band (CB) radio communications among truckers and general walkie-talkie operations. Truckers adopted ten-codes in the mid-20th century for CB radios to share road information efficiently, with slight modifications from police versions to fit their needs, such as 10-73 for "speed trap" or 10-200 for "police needed," contrasting with law enforcement's more formal interpretations focused on operational status and emergencies. In general walkie-talkie communications, ten-codes are used for brevity in two-way radios across various contexts like construction, recreation, and amateur use, often drawing from APCO origins but varying by region or group; for example, 10-4 universally means "message received," but specialized meanings like 10-100 for restroom breaks appear in informal settings, differing from professional police applications. These civilian variations, popularized by media and pop culture, enhance quick exchanges but can lead to confusion when interfacing with official systems due to non-standardized adaptations. Such variations have led to notable inter-agency communication challenges, particularly during multi-jurisdictional responses in the 1990s, when mismatched codes delayed coordination in joint operations like disaster relief and pursuits spanning agency boundaries. For example, differing interpretations of codes like 10-88—meaning "officer needs help" in one agency but a routine request in another—could result in critical delays or misunderstandings in mutual aid scenarios. These issues were exacerbated by the proliferation of localized codes without national oversight, contributing to broader interoperability failures observed in events like the 1982 Air Florida Flight 90 crash, where 19 agencies' unique protocols hindered effective response.

International Usage and Modifications

Outside , ten-codes have seen limited but notable adoption in emergency services, often adapted to local communication needs and hybridized with indigenous brevity systems. While originating from U.S. police practices, these codes have been modified in various regions to accommodate linguistic, operational, and cultural contexts, though full standardization remains rare due to preferences for or alternative protocols. In radio communications have incorporated a simplified version of ten-codes since at least the mid-20th century, primarily for indicating unit status and procedural messages, retaining core U.S.-inspired elements like affirmative acknowledgments while aligning with British-influenced emergency response frameworks. The employ a basic set of these codes within their Computer Assisted Dispatch system, such as 10-0 for "off duty," 10-1 for "broadcast to all units," 10-2 for "en route to job," 10-3 for "available," and 10-4 for "repeat last message." This adaptation emphasizes brevity in high-volume radio traffic, with some codes like 10-5 ("out of service") marked as obsolete since 1997 to streamline procedures further. The represents a more integrated adoption, where the (PNP) officially employs APCO ten-codes as part of its standardized radio communication protocol for and coordination with fire services. These codes facilitate rapid reporting across the archipelago's dispersed units, with examples including 10-4 for acknowledgment and 10-33 for emergency traffic. Complementing this, the volunteer-led TxtFire Foundation has incorporated ten-codes into its SMS-based fire alert system since its inception in the early 2010s, enabling civilians and responders to report incidents via text messages for faster mobilization in urban and rural areas. Adoption elsewhere in and has been sporadic and often partial, with ten-codes hybridized alongside local systems rather than fully replacing them. In other Asian contexts beyond the , such as parts of , ten-codes appear in informal or training materials for police and fire units but are typically blended with national brevity phrases, with no widespread standardization reported. International modifications of ten-codes frequently arise from cultural and linguistic barriers, necessitating adjustments to ensure clarity in multilingual or non-English-dominant environments. For instance, in the , protocols have been extended to include context-specific additions for tropical hazards like typhoon-related fires, diverging from core U.S. sets to address local disaster patterns. Such adaptations highlight broader challenges, including translation inconsistencies that can lead to miscommunication during joint operations and the need for training to bridge phonetic differences in radio transmissions. These factors have contributed to hybrid systems in regions like and , where ten-codes supplement rather than supplant to mitigate risks of ambiguity.

Applications in Emergency Services

Implementation in Police Operations

In police operations, ten-codes are integrated into routine dispatch sequences to facilitate efficient status updates and coordination among and dispatchers. For instance, an going off duty might transmit "10-7" to indicate being out of service, followed by "10-8" upon returning to active , ensuring dispatchers maintain accurate tracking of available units without lengthy verbal explanations. During traffic stops, codes such as "10-37" for a suspicious or "10-29" for checking a plate allow to quickly request information while minimizing airtime on shared frequencies. In suspect handling, "10-15" may signal a civil disturbance or in custody, prompting immediate resource allocation like additional units for transport or containment. Emergency protocols leverage ten-codes to prioritize critical situations and clear communications channels. The code "10-33" is employed to declare an , instructing all non-essential to cease and directing full to the transmitting unit during active threats, such as pursuits or confrontations. Escalation occurs if an officer is incapacitated, often via "10-00" to alert all patrols of an officer-down scenario, triggering an all-units response for rapid backup and medical aid. These protocols ensure swift, unambiguous alerts that can save lives by reducing response times in high-stakes incidents. Training and guidelines for ten-code usage are outlined in APCO resources, emphasizing etiquette to prevent frequency overload and miscommunication. Officers learn brevity rules through manuals like the APCO Operating Procedure Manual, which stress concise transmissions—such as avoiding unnecessary acknowledgments beyond "10-4"—to keep channels open for urgent calls. Initial academy training includes simulations of dispatch scenarios, reinforcing proper sequencing and code application, while ongoing refreshers address local variations to maintain procedural consistency. Historically, the 1970s-1990s marked a pivotal shift in police reliance on ten-codes as teletype systems gave way to voice radio dominance, driven by advancements in portable two-way radios that demanded faster verbal exchanges. Prior to this, teletype allowed written dispatches, but voice adoption necessitated codes for brevity amid limited bandwidth and static-prone channels. APCO Project 14 in 1974 expanded the codes to standardize procedures, enhancing speed during the era's increasing urban patrols and multi-unit responses. This transition solidified ten-codes as essential tools for until concerns prompted later reforms.

Use in Fire and Medical Response

In fire departments and emergency medical services (EMS), ten-codes enable concise radio transmissions during incident response, allowing responders to convey critical details like alarm types, unit status, and scene conditions without lengthy descriptions. These codes are integrated into dispatch protocols to coordinate apparatus deployment, resource allocation, and on-scene operations, often alongside mutual aid agreements that facilitate inter-agency support during large-scale incidents. Fire-specific ten-codes, drawn from agency-adopted lists rather than uniform NFPA standards, include 10-70 to signal a alarm, 10-71 to report the of the (such as or involvement), and 10-82 to indicate a in progress, prompting immediate apparatus dispatch. Additional codes like 10-76 (en route) and 10-77 ( duty assignment) support coordination, while post-1980s adaptations in some departments incorporated codes for hazmat incidents to address chemical or hazardous material responses. Response procedures emphasize staging with 10-23 (arrived at scene) to position units safely before engagement, followed by 10-24 (assignment completed or all-clear) once the incident is resolved, ensuring orderly demobilization. In EMS integrations, ten-codes facilitate medical dispatches by specifying patient conditions and transport needs, such as 10-52 (ambulance needed) for urgent calls and 10-55 (intoxicated driver) to alert responders to potential behavioral or overdose scenarios requiring specialized handling. These are often combined with fire response in combined dispatch centers, where codes like 10-56 (intoxicated pedestrian or suicide) trigger integrated EMS-fire teams under mutual aid protocols to manage scenes involving medical emergencies alongside fire risks. An example of ten-code adaptation in resource-limited settings is the TxtFire system, which uses SMS-based alerts for rural response through volunteer networks; it employs -tailored codes like 10-70 ( alarm), 10-71 (nature/situation of ), and 10-73 (add apparatus/engine) to mobilize community responders via text, with operational guidelines restricting transmissions to emergencies, requiring clear English or Tagalog usage, and limiting calls to three minutes unless ongoing. This approach enhances coordination in areas with poor radio infrastructure, integrating volunteer brigades under national frameworks.

Decline and Modern Alternatives

Transition to Plain Language Protocols

The transition from ten-codes to plain language in emergency communications was driven primarily by the need for enhanced following the , 2001, terrorist attacks, which exposed significant communication barriers among responding agencies. The Department of Homeland Security (DHS) emphasized eliminating like ten-codes to facilitate clearer exchanges during multi-agency operations, as variations in code meanings across jurisdictions often led to confusion. In 2005, federal guidelines tied to funding eligibility required to adopt , marking a key push amid post-9/11 reforms aimed at national standardization. By 2006, the (NIMS) Integration Center, under FEMA and DHS, issued a formal alert mandating the use of in multi-agency, multi-jurisdiction, and multi-discipline incidents to replace ten-codes and other brevity codes, citing their role in hindering effective coordination. This directive built on earlier efforts by the Association of Public-Safety Communications Officials-International (APCO). The timeline of adoption accelerated with federal initiatives in the 2000s. By the early 2010s, widespread implementation took hold, with major agencies such as the Washington County Sheriff's Department in transitioning in 2010 to align with NIMS requirements. Most U.S. emergency services agencies had shifted to protocols by the mid-2010s, supported by DHS training resources and CISA guidelines. A primary benefit of this shift has been the reduction of errors in multi-agency responses, where differing interpretations of ten-codes previously caused delays and misunderstandings. For instance, during in 2005, out-of-state responders encountered code variations that complicated coordination, prompting FEMA to recommend to prevent such issues and enabling quicker reversion to direct speech for clarity. This change has improved and response times in joint operations, as eliminates the need for code training across agencies. Despite these advances, the transition remains incomplete as of 2025, with ten-codes lingering in some rural and legacy systems due to resistance from long-established practices and limited resources for retraining. agencies in smaller jurisdictions often retain codes for internal use, even as federal mandates prioritize for . In general radio uses such as CB radios among truckers and walkie-talkies, ten-codes continue to be widely employed, with the emphasis on improved clarity and interoperability through plain language being more relevant to emergency services but increasingly recognized in broader communication contexts.

Brevity Codes and Standardized Clear Text

In response to the limitations of ten-codes, the Association of Public-Safety Communications Officials (APCO) developed the Phrase Word Brevity Code (PWBC) in the late as a standardized set of short, plain-language phrases to facilitate clearer radio communications among public safety agencies. The PWBC aimed to reduce misunderstandings caused by varying interpretations of numerical codes across different jurisdictions, enabling faster integration of personnel and improved by replacing phrases like "10-4" with equivalents such as "Affirmative" or "Negative." Examples include "Use Caution" for situations requiring vigilance (corresponding to older 10-29), "Out of Service" for units going offline (10-7), and "Available" for ready status (10-24), promoting brevity while prioritizing comprehension over coded brevity. Although introduced earlier, the PWBC gained renewed emphasis in the as part of broader plain-language initiatives, influencing modern protocols in U.S. emergency communications. Complementing such efforts, the (ICS) under the (NIMS), established in 2004, mandates the use of clear text— without codes or —to ensure effective coordination during multi-agency incidents. This standard, reinforced in the 2008 NIMS update following lessons from , requires all organizational elements to communicate in clear text for interoperability, restricting messages to essentials and prohibiting agency-specific acronyms to avoid confusion in high-stress environments. A representative example is "All units stand by," used to halt transmissions and await instructions during emergencies, ensuring universal understanding across disciplines like police, , and EMS. ICS clear text also incorporates reinforcements such as the (e.g., "Alpha" for A) to clarify spellings or identifiers, enhancing accuracy in noisy or complex scenarios without relying on obsolete codes. Some regional systems retain limited signal-based brevity as transitional tools within clear-text frameworks; for instance, "Signal 1" denotes an needed in certain fire and EMS operations, serving as a concise alert while aligning with plain-language mandates. of these brevity codes and clear-text standards has been widespread, driven by federal requirements for NIMS compliance, with most U.S. states and territories implementing plain-language protocols by the early to improve response times and . Internationally, similar shifts emphasize plain English to mirror these advancements. In the , the rollout of the Airwave digital radio network beginning in 2001 prompted emergency services to abandon coded phrases in favor of , using nationally agreed terms for radio transmissions to enhance multi-agency collaboration. This approach, formalized in guidelines like those from the , requires "only and nationally agreed terms" during operations, influencing global standards such as those in the European Union's emergency communications frameworks.

Cultural and Broader Impact

Ten-codes have been a staple in American television and film since the mid-20th century, often dramatized to heighten tension in police procedurals and action sequences. The 1950s series , starring , was among the first to incorporate ten-codes into broadcasts, introducing phrases like "10-4" (acknowledgment) to a wide and embedding them in as authentic police lingo. Similarly, 1970s shows such as and frequently featured officers exchanging codes over radio during pursuits and routine calls, portraying them as essential for rapid, efficient communication amid chaos. These depictions emphasized brevity and urgency, with codes like "10-50" (accident) or "10-8" (in service) underscoring the high-stakes nature of . In cinema, ten-codes appear in high-action contexts to convey procedural realism. For instance, in (2007), protagonist deliberately misuses a ten-code over to expose an imposter dispatcher, highlighting their role in verifying authenticity during crises. Such scenes reinforce the codes' mystique, blending technical jargon with narrative suspense. In contemporary television, series such as The Rookie (2018–present) continue to depict officers using ten-codes in radio communications, maintaining their presence in portrayals of procedures. Beyond emergency services, ten-codes permeated broader pop culture through CB radio slang in the trucker subculture, immortalized in the hit song "" by and its 1978 film adaptation, where "10-4, good buddy" became a for affirmation among drivers evading authorities. This adoption spawned memes, merchandise, and casual usage in everyday speech, extending the codes' reach far beyond professional radio use. The influence of such media depictions led to the widespread adoption of ten-codes in general walkie-talkie communications, where they are used by civilians for brevity in two-way radio exchanges, often mirroring trucker and police variations with slight adaptations for non-emergency contexts, such as "10-20" for location queries. This cultural permeation, driven by trucker subculture and popular media, has made ten-codes a staple in recreational and informal radio use, though meanings can vary by region or user group. However, these portrayals have drawn for fostering inaccuracies. Media often presents ten-codes as universally standardized, ignoring regional and agency variations that can lead to real-world miscommunications, a concern amplified in analyses of public safety protocols pushing for alternatives. This dramatization contributes to public misconceptions, such as assuming all officers nationwide share the same code meanings, potentially complicating inter-agency responses. Q-codes, a set of three-letter abbreviations beginning with "Q," originated in 1909 when the British government developed them for use in maritime radiotelegraph communications between ships and coast stations to ensure clarity in international transmissions. These codes were later adopted by operators and services, with examples like QSL meaning "I acknowledge receipt" or "confirmation of communication." Unlike the numeric structure of ten-codes, which emphasize quick verbal numbering for brevity, Q-codes rely on alphabetic combinations for procedural and operational , facilitating efficient exchanges in noisy or international environments. Prior to the widespread adoption of ten-codes in the , some U.S. fire departments employed signal codes or numbered response protocols to coordinate apparatus dispatch and incident types. Variants such as 12-codes emerged in regional public safety communications, particularly in and contexts, extending beyond the standard 10-series with additional numeric signals for routine status updates, though their use varied by agency and predated national standardization efforts. In the 1970s, during the Citizens Band (CB) radio boom fueled by the oil crisis and trucking culture, civilians adapted ten-codes for non-emergency use, extending the original police lexicon with informal additions suited to highway and personal communications. Popular examples included 10-200 to signal "police needed," reflecting a blend of official brevity with trucker slang that popularized terms like "10-4" in mainstream media. This civilian extension highlighted ten-codes' versatility beyond professional services, though it also led to inconsistencies as users improvised local variations. Modern relatives of ten-codes include the , standardized in 1956 for spelling clarity in and adopted universally for radio procedures, and tactical brevity words, which use concise terms like "" for missile launches in joint operations. Post-2000 updates to NATO's Allied Procedural Publication 7 (APP-7) integrated these with evolving technologies, such as secure digital comms, to enhance across multinational forces while maintaining brevity in high-stakes environments. These systems parallel ten-codes by prioritizing rapid, unambiguous exchanges but emphasize phonetic and procedural standardization over numeric coding.

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