The equals sign was born from a writer's impatience

Before 1557, mathematicians spelled out equality in longhand. Then Robert Recorde, a Welsh physician and mathematician, grew tired of it. In The Whetstone of Witte — the first English book to use the + and − signs — he introduced a new shorthand.

To avoid the tedious repetition of the words is equal to, he wrote, he would set down a pair of parallels, or Gemowe (twin) lines of one length: =.

Bicause noe 2 thynges can be moare equalle.

His reasoning was almost poetic: nothing could be more equal than two identical parallel lines. The symbol wasn’t an instant hit — rivals used other marks well into the 1700s. Recorde never saw it win; he died in a London prison in 1558. Today his two little lines sit in every equation on Earth.