A pressure gauge is an instrument used to display the pressure of a fluid. The most widely used type of pressure gauge is the Bourdon gauge which uses a flattened tube that tends to straighten or regain its circular form with change in pressure. The flattened tube is directly coupled with the a mechanical arm that directly drive the needle of the display. Bourdon tube pressure gauges are fitted with a magnet on the Bourdon tube itself so that as pressure increases, the magnet moves along a circumference. A circular PCB with multiple reed switches mounted from radial center to circumference, wired to generate a potentiometric two wire feedback is triggered by the magnet as the pressure changes. Circuits for such PCBs follow the same principles of level sensors, which is reed switches combined with resistors, and more information can be found here. This sort of assembly is cost effective and accurate. An added advantage in such gauges is that multiple alarm points can be set and the digital outputs can be saved to a web server or to a smart phone.