reckoner

A handbook of mathematical tables used to facilitate computation.

One who reckons or computes: as, a rapid reckoner.

Something that assists a person to reckon or cast up accounts, as a book containing a series of tables; a ready-reckoner.

One who reckons or computes; also, a book of calculations, tables, etc., to assist in reckoning.

One who reckons.

An accountant.

an expert at calculation (or at operating calculating machines)

a handbook of tables used to facilitate computation