“
Robert Recorde invents the equals sign


I mentioned recently that
the integral sign is actually a letter
"S", chosen by Leibnitz because it was the first letter of the word
"sum". Seth David Schoen suggested that Leibnitz probably wrote in
Latin, so that it is actually the first letter of the word "summa",
which means "sum" in Latin. I do not know, but I will see if I can
track down the original paper.” source...