It was not uncommon to draw a line through the zero to distinguish it from the letter ‘O’. Similarly, a slash was often added to the letter ‘Z’ to prevent confu

It was not uncommon to draw a line through the zero to distinguish it from the letter ‘O’. Similarly, a slash was often added to the letter ‘Z’ to prevent confusion with the number 2. On rare occassions, I still kind of do it.