You have to measure the tyre height mounted, with air in it (at the specified pressure on the specified rim width to be exact) and not loaded (ie. OFF THE CAR!). Not on the Jeep and loaded... drives me crazy when people do this and then complain about the tire not being the 'true height'...
The proper way to measure the height is to measure the circumference around the centre of the tire (yes, mounted and aired up... but not loaded), and calculate the diameter.
Your Procal (or whatever you use) really cares about tyre circumference - not height at a given pressure and a given vehicle weight etc. When its on the vehicle, taking air out, or putting more air in, will change the height of the top of the tyre... but it won't change its rolling circumference. 10 rotations will basically take you the same distance at 10psi or 35psi, even though the tire height will be different.
Please, please, pleeeeeeaaaaase stop measuring tire heights when loaded... for the sake of my sanity...
S.