Pirani gauge was invented by Marcello Pirani in 1906.[1] This gauge is employed to measure pressure at low vacuum, e.g. those obtained by rotary pumps, based on thermal conductivity. The gauge is composed of a thin, heated tungsten wire that is exposed to the vacuum. At poor vacuum, many gas molecules interact with the wire, and thus conduct heat away quickly, resulting in lower resistance of the wire because of lower temperature; therefore, a high electrical current through this wire is induced. At better vacuum, fewer gas molecules interact with the heated wire, and thus conduct heat away slowly, resulting in a higher wire's resistance and lower electrical current. Since the flow of the electrical current through the wire depends on the level of vacuum, it can be calibrated to evaluate the actual vacuum level.