Calculator
Part of speech: noun
Definition: A person who performs mathematical calculation A person who calculates (in the sense of scheming). A mechanical or electronic device that performs mathematical calculations. A set of mathematical tables.
Example sentence: Nothing ruins the lines of a suit or blazer and makes you look more like a doofus than when your pockets are crammed with stuff - a wallet, a cell phone, keys, a calculator, a calendar, pens, etc.
Reckoner
Part of speech: noun
Definition: One who reckons.An accountant.