Free, instant, and no sign-up. The maths behind these is tested against published figures rather than eyeballed.
Because the questions come first. Nobody searches for a chip set until they have worked out how many chips they need, and nobody prints a blind structure until they have decided how long the night should run. These are the tools we would want ourselves, so they are free and there is nothing to sign up to.
Where a tool touches something we sell, it says so — the chip calculator counts in the pack sizes we stock, because counting in anything else would be useless when it came to ordering.