Equal sign commonly used in mathematics and computing around the world, was first recorded by welsh mathematician Robert Recorde in 1557 in his book “The Whetstone of Witte”. Recorde composed the symbol consisting of two parallel lines to avoid having to write over again and again “is equal to”. Recorde’s representation of the equal sign consisted of two long parallel lines. It took around 150 years before the cocept became popular. In 1700s some people used the symbol || , while others widely used the symbols- æ or œ (derived from latin word aequalis / equal).
Below is the snippet from the book where Robert Recorde introduced the equal sign for the first time.
“To avoide the tediouse repetition of these woordes: is equalle to: I will settle as I doe often in woorke use, a paire of paralleles, or gemowe [twin] lines of one lengthe: =, bicause noe .2. thynges, can be moare equalle.”