0: Numeric zero, as opposed to the letter `O' (the 15th letter
of the English alphabet). In their unmodified forms they look a lot
alike, and various kluges invented to make them visually distinct
have compounded the confusion. If your zero is center-dotted and
letter-O is not, or if letter-O looks almost rectangular but zero
looks more like an American football stood on end (or the reverse),
you're probably looking at a modern character display (though the
dotted zero seems to have originated as an option on IBM 3270
controllers). If your zero is slashed but letter-O is not, you're
probably looking at an old-style ASCII graphic set descended from
the default typewheel on the venerable ASR-33 Teletype
(Scandinavians, for whom /O is a letter, curse this arrangement).
(Interestingly, the slashed zero long predates computers; Florian
Cajori's monumental "A History of Mathematical Notations" notes that
it was used in the twelfth and thirteenth centuries.) If letter-O
has a slash across it and the zero does not, your display is tuned
for a very old convention used at IBM and a few other early
mainframe makers (Scandinavians curse _this_ arrangement even more,
because it means two of their letters collide). Some
Burroughs/Unisys equipment displays a zero with a _reversed_ slash.
Old CDC computers rendered letter O as an unbroken oval and 0 as an
oval broken at upper right and lower left. And yet another
convention common on early line printers left zero unornamented but
added a tail or hook to the letter-O so that it resembled an
inverted Q or cursive capital letter-O (this was endorsed by a draft
ANSI standard for how to draw ASCII characters, but the final
standard changed the distinguisher to a tick-mark in the upper-left
corner). Are we sufficiently confused yet?
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