Boyle's law

Boyle's law is a special case of the ideal gas law from which one may calculate either the pressure or the volume of gas. It was developed by Robert Boyle in the 1660s and describes any inverse relationship between the pressure (P) and the volume (V) of a given amount of gas at a fixed temperature.

Boyle's law $\left(PV\right)=constant$ (at fixed temperature and amount of gas)