John Cowan wrote:

>
> Marco Cimarosti scripsit:
>
>> It does actually also have that utilitarian function of avoiding
>> modification of the text, but that's also true of, e.g., the diagonal
>> line often seen on Western digit zero, or the crossbar seen on digit
>> seven:
>
> As I understand it, these are for disambiguation rather than security:
> 0 vs. O, 7 vs 1 (in styles where 1 has an upper serif but no lower
> serif). North Americans, as you probably know, write 1 as a simple
> vertical line and do not cross 7.

True, and we often draw a horizontal bar through Z
to distinguish it from the digit 2.

When I was in college in the 1970s, we were taught
to put the slash on the letter O and leave the zero
alone. But everyone else seemed to slash the zero.

In the days of dot-matrix printers, people often
misread slashed-zero as the digit eight, especially
if the dots were a bit out of alignment. One company
I worked for actually had me write a routine which
would intercept data to the printer, and substitute
a letter O for the zero because of this.

--Ph. D.