Actually 0-7. Three bit octal. All transponder codes are four digits - each
digit is 0-7. Technology comes VERY slowly to aviation.


"Mike Granby" wrote in message
...

I find myself holding a 747 transponder control head that I bought on
eBay as a toy for the kids. But, with echos of Spinal Tap's guitarist
in my head, I notice that the selector knobs allow the digits 0 thru 8
to be selected. What gives?