Schoolmaster and amateur mathematician William Shanks (1812–82) spent the greater part of his life working out the value of pi (the ratio of a circle’s circumference to its diameter) to 707 decimal places. More than 60 years after his death, mathematician DF Ferguson, using a mechanical calculator, pointed out that he had got the last 180 of these decimal places wrong.
In the late 1940s an ENIAC computer took 70 hours to calculate 2,037 digits of Pi. In 1958 an IBM computer did in 40 seconds what Shanks had done in a lifetime. The millionth digit of pi was found in 1973 and the billionth by 1995.
Sources: History Extra