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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 slashed-O is a letter, curse this
   arrangement).  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.  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.  Are we sufficiently confused yet?