The Gregory-Leibniz Series is a way to calculate pi. It goes like this: (4/1) - (4/3) + (4/5) - (4/7) + (4/9) - (4/11) + (4/13) - (4/15)... The more iterations you do, the more accurate your result of Pi is. Gregory-Leibniz Series is NEVER used for large scale operations to discover new digits of pi because it takes a really long time to converge.