Where did 10 4 originate like on cb radio

Question

Where did 10 4 originate like on cb radio

Answer 1

"understood" or "affirmative"

10-20 means 'what's your location?'

Answer 2

Ten-codes were developed in the 1940s

Credit to the originator goes to Charles "Charlie" Hopper. He was the Communications Director at the Illinois State Police, District 10, located in Urbana, Illinois.

Answer 3

APCO "10" Codes

10-Codes

Association of Public Safety Communications Officers or APCO developed the 10-Codes in 1937 and expanded them in 1974.

Used for brevity and security by many agencies.  The APCO 10-Codes are a standardization set of codes designed to facilitate communications between different agencies.  Many agencies use some or all of those codes.  Other informal codes and abbreviations, unique to each agency, are often heard.

Oldest and largest association of public safety personnel, they are the authors of Project 16, Project 25 and designated FCC frequency coordinator for the Public Radio Service, the Local Government Radio Service and the Public Safety "pool" of frequencies in the 800MHz band.

10-Codes

These codes are used by police. Each code represents a phrase.

10-0  use caution

10-1  poor reception

10-2  good reception

10-3  stop transmitting, change channels

10-4  message received, affirmative, ok, understood

10-5  relay this information to ___  

Up to 10-99