I never said slashed zeros were unknown, just that conventions hadn't settled yet and were far from universal. Sometime you got a dot in the middle instead of

I never said slashed zeros were unknown, just that conventions hadn't settled yet and were far from universal. Sometime you got a dot in the middle instead of a slash. I don't know if OCR even existed back when this was published. If it did, it wasn't common. The manual typewriter I learned to type on did not have a zero or one.