Symbols for zero

The modern numerical digit 0 is usually written as a circle, an ellipse or a rounded square or rectangle.

Traditionally, many print typefaces made the capital letter O more rounded than the narrower, elliptical digit 0.

An alternative, the slashed zero (looking similar to the letter O except for the slash), was primarily used in hand-written coding sheets before transcription to punched cards or tape, and is also used in old-style ASCII graphic sets descended from the default typewheel on the Teletype Model 33 ASR.

The opposing convention that has the letter O with a slash and the digit 0 without was advocated by SHARE, a prominent IBM user group,[1] and recommended by IBM for writing FORTRAN programs,[2] and by a few other early mainframe makers; this is even more problematic for Scandinavians because it means two of their letters collide.

The typeface used on most European vehicle registration plates distinguishes the two symbols partially in this manner (having a more rectangular or wider shape for the capital O than the digit 0), but in several countries a further distinction is made by slitting open the digit 0 on the upper right side (as in German plates using the fälschungserschwerende Schrift, "forgery-impeding typeface").