Equals sign

For the binary relation, see ==.

= and ＝ redirect here. These characters are also used as a double hyphen in some character sets.

:= leads to this page. This symbol is used for definitions.

The equal sign, equals sign, or = is a mathematical symbol used to indicate equality. It was invented in 1557 by Welshman Robert Recorde. The equals sign is placed between the things stated to be equal.

The = symbol that is now universally accepted in mathematics for equality was first used by Welsh mathematician Robert Recorde in The Whetstone of Witte (1557). The original form of the symbol was much wider (longer) than the present form. In his bookRecorde explains his design: to avoid the tediouse repetition of these woordes: is equalle to : I will sette as I doe often in woorke use, a pair of paralleles, or Gemowe lines of one lengthe, thus: =, bicause noe .2. thynges, can be moare equalle. According to Scotland's St Andrews University Maths History website[http://www-history.mcs.st-and.ac.uk/Mathematicians/Recorde.html" target="_blank" >^*, "The symbol = was not immediately popular. The symbol || was used by some and æ (or œ), from the Latin word aequalis meaning equal, was widely used into the 1700s."

The invention of the equals sign is commemorated in St. Mary's Church, Tenby, Wales.

A symbol used to denote items that are approximately equal is ≈, and the symbol used to denote when items are not equal is ≠; (most programming languages, which are limited to the ASCII character set, use "!=", "=/=" or "<>" to represent "not equal to"; "!=" has carried over into newsgroups and Internet forums). The symbol ≡ is often used to indicate an identity, or a congruence relation in modular arithmetic.

In programming languages, the equal sign may either denote a boolean operator to test equality of values (sometimes a double equal sign

false) is true, but (0 false) isn't.)

Boyer, C. B.: A History of Mathematics, 2nd ed. rev. by Uta C. Merzbach. New York: Wiley, 1989 ISBN 0-471-09763-2 (1991 pbk ed. ISBN 0-471-54397-7)

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