Info (click to close)
 Newlines and spaces seperate words.
 Words can be numbers or operators.

A number is any PHP numerically parsable string, i.e. most things work.
This will be pushed to the stack.

An operator is either one of
+*/%
. You know how those work, you know primary school math. (okay well maybe not for %
modulo)
They assume some numbers on the stack, pop them, and push the result.
 See more at Wikipedia.
 If you don't have JavaScript disabled, you can use Shift+Enter on the input to calculate, and Shift+Up anywhere to carry result.
Also known as: Ćukasiewicz notation, Polish postfix notation, postfix notation.
May or may not work.