The EDO Artisan 1200 series indicators were designed to meet stringent requirements of monitoring pressure losses in helicopter rotor blades. However, they may be applied to any closed fixed volume pressure or vacuum system where changes in the pressure of the gas are to be monitored. They do not use springs or other conventional means of pressure monitoring. Instead, a proprietary bellows technology is employed, which yields an exceptionally accurate and reliable measurement. These instruments are unique in that there is a "reference pressure" contained internally, which is completely independent of the system being monitored. When installed, they become an integral part of the system. This "reference pressure" when calibrated to the system becomes a standard to which the system pressure is measured. A loss of system pressure within the specified limits creates an unbalanced condition between the "reference pressure" and the system pressure, thereby resulting in a visual indication. A visual and remote indication is also in certain models. This unique method also accounts for the temperature compensation feature.