I recorded the "calibrated" pressure reading taken at the IMC vent/purge connection and compared it to the time-corresponding pressure indicated by PT120A (pirani gauge) all while in pressure equilibrium [0.6 psi versus PT120A indicated value of 941.5 torr].  Recall that we have documented a known problem with PT120A's indicated pressure values for high pressure conditions.  We had tried multiple sensor heads and minimized the ATM potentiometers but just can't get the CDS read back to agree with the known conditions.  For some unknown reason, it is always indicating a much higher pressure than the actual pressure.  We eventually "moved on" but resolved to work with EE/CDS at some point to figure it out (low priority at the time).  

I also measured the maximum pressure available from the purge-air supply using the "fancy" mechanical gauge and measured 1.2 psi maximum.  This agrees with the maximum value ever observed at the mechanical gauges at the output of the purge air supply skid and gives us confidence that we haven't over-pressurized the vacuum system (read "view ports").