Five by Five

Five by Five

 As seen at Pain In The English

Where does the term 'five by five' come from? I first heard it on 'Buffy the Vampire Slayer', but have since heard it in a military setting. The context on 'Buffy' is:

How are you doing?
Five by five!

I take it to mean something like 'fine', 'great' or something similar. Does anyone know how it came to be?.. read more