Ted - Actually the gauge in the steering compartment is pretty close to the digital.
Jon - Some of the old trucks used to have a pressure gauge in the dash group for brake pressure and I thought that was was good. It wouldn't be too difficult to tap into the brake system and this gauge can read two different pressures by installing a single throw double pole switch. It would be easy to see how much pressure it takes from the aux to move air bags, so I may do a little experimenting while hooked up to shop air.