regular costumer; patron

to use one's head

(mathematics) a kind of grid used in 和算 (wasan, “traditional Japanese mathematics”) to calculate higher-order functions / (mathematics) an abacus

everything

(colloquial) current boyfriend

(slang) Alternative form of 彼氏 (kareshi, “boyfriend”)

everyone, one and all

a machine used for performing calculations; a calculator / computer

spreadsheet - manual calculation of digits in the grids / (computing) spreadsheet - automatic calculation of digits in the grids by using computer.

calculating