Here's one for the tecchies ...
The VC10s I used to fly in the 1970s (or was it the early 747s, I can't remember now) had selectable transponder digits (!) which all ran from 0 to 8 (yes eight) inclusive. By experimenting, we found that setting an 8 seemed to produce the same result as if a 0 had been set.
I asked many people at the time why/how the numbers could run beyond 7 as the system was octal but was never offered a plausible explantion.
Maybe someone out there may now have an answer ... ?
JD