What does "mental calculation" mean?

Arithmetical calculations using only the human brain, with no help from any supplies (such as pencil and paper) or devices such as a calculator.

Mental calculation

Common synonyms include: arithmetic basics, arithmetic strategy, basic calculation, head calculation, head math task, head-based calculation skill.

noun

noun ·Rare ·Advanced level

Noun

1
Arithmetical calculations using only the human brain, with no help from any supplies (such as pencil and paper) or devices such as a calculator. countable, uncountable