Copy That

Today is International Zookeeper Day, selected because... it's 10-4.  Which I never understood.  I mean, why zookeepers? Lots of jobs use radios and radio jargon, many of them which I associate much more with radios than zookeepers.

Also, it's interesting that you rarely hear other ten-codes besides 10-4, which, weirdly, has exactly as many syllables as "OK" so isn't saving anyone any time in using it.  Sometimes I'll hear people use 10-20, "What's your 20?" as in "Where are you?" but other than that, none of the others.  Which got me curious - what do the others mean, and would any of them be applicable to our work?