Equals sign

The equal sign, equals sign, or =, used to indicate the result of some arithmetical operation, was invented in 1557 by Robert Recorde.

The = symbol that is now universally accepted for equality was first used by Robert Recorde in The Whetstone of Witte (1557). In the book (See image of page[1] (http://members.aol.com/jeff94100/witte.jpg)), he 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 [ie twin] lines of one lengthe, thus: =, bicause noe 2 thynges, can be maore equalle. According to the St Andrews University Maths History site[2] (http://www-history.mcs.st-and.ac.uk/Mathematicians/Recorde.html), " The symbol = was not immediately popular. The symbol || was used by some and æ (or œ), from the word 'æqualis' meaning equal, was widely used into the 1700s."

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

The symbol used to denote when something is approximately equal to something else is ≈, and the symbol used to denote when something is not equal to something else is ≠. The symbol ≡ is often used to indicate an identity rather than an equation.

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