10-4 CB lingo. Help me out here.

[awty]

Long before CBs became a thing that truckers and the average Joe had my dad had a two-way radio with the base station and a HUGE antenna tower at the home office and he had a radio in his truck. He was a veterinarian who mostly traveled from farm to farm treating dairy cattle and hogs. We were trained early how to use the radio. I still remember the routine. The call letters were KLW272 - there was no nickname like later on the CB when many people had access to the same radio bands. Dad would call in and we would either respond with new calls that had come in or we would say 'nothing doing'. Every call ended with 10-4 from either dad or whoever at the house had answered the call. I always saw '10-4' as being similar to hanging up the phone - this conversation is over - nothing more to follow.