Zu Chongzhi was the first to calculate pi to seven decimal places.
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history
5th-century mathematician 祖冲之 calculated 3.1415926 < π < 3.1415927 - the most accurate value in the world for nearly 1,000 years. Earlier, 刘徽 used the 割圆术 ('circle-cutting method') to approximate π ≈ 3.14, called the 徽率 in his honor.
memory
Decompose: 圆 (circle) + 周 (circumference) + 率 (ratio) - literally 'circle-circumference-ratio'. Note 率 here is lǜ (fourth tone, 'ratio'), not shuài ('to lead').
