also: ひゃくマスけいさん
noun
100-square calculation; grid-based arithmetic drill
A learning method using a 10×10 grid for repetitive practice of basic arithmetic (addition, subtraction, multiplication, etc.), often used in Japanese elementary schools to build speed and accuracy.
毎朝、百ます計算をしてから授業が始まります。
Every morning, class starts after doing 100-square calculations.
百ます計算でかけ算の練習をすると、暗算が速くなります。
Practicing multiplication with 100-square calculations makes mental arithmetic faster.
計算ドリル is a general arithmetic workbook, while 百ます計算 specifically refers to the 10×10 grid drill method.
From 百 (hundred) + ます (square, cell) + 計算 (calculation), referring to the 100 cells in the 10×10 grid used for the drill.