Eventually the dual inlet bellows may not fully expanding to 100%, leading to a lower pressure and signal when compressed, than if they had been fully expanded before putting in the sample.

The check:
  -Exactly equalize pressure for both bellows when they *claim* to be 100%
  -Compress both to the same claimed volume say 20%
If there is a pressure mismatch, the one with lower P was not expanded as much as the other when claiming to be 100 (although BOTH may have not fully expanded.)

The fix:
  -Set both at 100% in isodat
  -Remove the o-ring belts from the brass pulleys on the potentiometers
  -Rotate the pulleys fully clockwise until they hit their internal stop
  -Put back the o-rings
  -Run the bellows calibration macro in isodat

Bob's your uncle.

-J