These gauges are intended for measuring the pressure differential existing across two media or two parts of a system. All common pressure elements are used, as the application demands. The pressure element separates the two pressurised media, and deflects proportional to the difference in pressure between the media, irrespective of the absolute pressure applied. This deflection is converted into the rotation of a concentric pointer on a dial, similar to regular pressure gauges. The absolute value of either of the pressure is not usually indicated.