The slashed zero is a representation of the Arabic digit "0" (zero) with a slash through it. The slashed zero glyph is often used to distinguish the digit "zero" ("0") from the Latin script letter "O" anywhere that the distinction needs emphasis, particularly in encoding systems, scientific and engineering applications, computer programming (such as software development), and telecommunications. It thus helps to differentiate characters that would otherwise be homoglyphs. It was commonly used during the punch card era, when programs were typically written out by hand, to avoid ambiguity when the character was later typed on a card punch. Usage The slashed zero is used in a number of fields in order to avoid confusion with the letter 'O'. It is used by computer programmers, in recording amateur radio call signs and in military radio, as logs of such contacts tend to contain both letters and numerals. The slashed zero was used on teleprinter circuits for weather applications. In this usage it was sometimes called communications zero. The slashed zero can be used in stoichiometry to avoid confusion with the symbol for oxygen (capital O). The slashed zero is also used in charting and documenting in the medical and healthcare fields to avoid confusion with the letter 'O'. It also denotes an absence of something (similar to the usage of an 'empty set' character), such as a sign or a symptom. Slashed zeroes can also be used on cheques in order to prevent fraud, for example: Changing a 0 to an 8. Slashed zeros are used on New Zealand number plates. History The slashed zero predates computers, and is known to have been used in the twelfth and thirteenth centuries. In the days of the typewriter, there was no key for the slashed zero. Typists could generate it by first typing either an uppercase "O" or a zero and then backspace, followed by typing the slash key. The result would look very much like a slashed zero. It is used in many Baudot teleprinter applications, specifically the keytop and typepallet that combines "P" and slashed zero. Additionally, the slashed zero is used in many ASCII graphic sets descended from the default typewheel on the Teletype Model 33. The use of the slashed zero by many computer systems of the 1970s and 1980s inspired the 1980s space rock band Underground Zerø to use a heavy metal umlaut Scandinavian vowel ø in