Hermann's Formula

The Machin-Like Formula

$${\textstyle{1\over 4}}\pi=2\tan^{-1}({\textstyle{1\over 2}})-\tan^{-1}({\textstyle{1\over 7}}).$$

The other 2-term Machin-Like Formulas are Euler's Machin-Like Formula, Hutton's Formula, and Machin's Formula.