It is PE measured psi, the most common unit now in use. LUP (based on lead crushers) and CUP (based on copper crushers) were in near universal use before PE and strain gauges became readily available. Lead is used for lower pressures and copper for higher. The trick was to match the crusher materials compressive strength to the pressure range anticipated. If the crushed was not significantly deformed, it was difficult to measure accurately. If overly deformed, it became inaccurate. Crushers can measure only peak pressure they are exposed to; a chamber mounted crusher will measure chamber peak pressure and a barrel mounted crusher will measure barrel peak pressure. PE and strain gauge measure near instantanious and can deliver time based curves of pressure build-up and decay. Crusher pellets must be made extreamly accurately or they have no value. Used to be that cartridge loaders bought certified crusher pellets in large volume.
PE and strain gauge readings will depend on the accuracy of system calibration. Crushers depended on the accuracy of the crusher pellet and the accuracy of the measurement of deformation. Crusher and electronic psi are not in strict agreement. 2-p gave a simple and effective conversion of LUP to PE psi.
