About

There is no server here. The pages are static files, the arithmetic is a script your browser downloads once, and nothing typed into a field leaves the machine it was typed on — not because of a policy, but because there is nothing on the other end to receive it.

The aim is narrow: be right, show the working, and load fast enough that you do not notice it loading. Where a calculation cannot be made honestly — a holiday this site does not know, a convention that differs by institution — the page says so rather than printing a confident number.

The rules are published in full on the how every figure is checked page, including how they are checked.