Florian Cajori

A Swiss-American historian of mathematics who became the world's leading authority on how mathematical symbols and conventions came to be the way they are. His two-volume A History of Mathematical Notations (1928–29) traced the evolution of every common symbol ($+$, $-$, $\times$, $÷$, the equals sign, the integral sign, even brackets) across centuries of practice. The order-of-operations conventions (BIDMAS / PEMDAS) that schoolchildren learn today are themselves the product of a long, gradual standardisation that Cajori was the first to document properly.