The introduction of "oh" as a reading of zero is certainly one of the most diabolical [diachronic!] developments of all time.

When I was in the Navy part numbers were formed of letters and numerals scattered helter-skelter, swept up and lined up in neat rows. There was no discernible rhyme nor reason to them. After various attempts to force some uniformity down craws already sated with uniformity the differences between O and 0 and between I and 1 were decreed to be meaningless.