Ten 1 : code A system of radio codes referring to the most commonly used messages. For example, 10-4 signals acknowledgment; 10-7, out of service; 10-8, in service; and 10-9, repeat
Ralph W. Burklin & Robert G. Purington, Fire Terms: A Guide to Their Meaning and Use, National Protection Association, Boston, MA 1980 USA. (Guide: Meaning and Use, Nat Prot Association Fr Srvc - Amer) {457}