thank you BD

I agree that the truck + trailer need to be level to get an accurate reading.....but as for the other stuff.....well I've charted ~100 readings on CAT scales in winter and summer and I've noticed no inaccuracies.

Cat scales don't use air pressure to measure the weight. They use load sensors which are basically a piece of metal that gets "squashed" when you drive on them. The computer reads the "amount of squashing" to give the weight.

I use 2 right weigh gauges mounted in the dash. They are within 500lbs. Also it's a good idea to get the truck/trailer level after they load you, because the scales will show 2,000lbs off depending on which is on the down side.
All in all my investment has almost paid for itself,...$200 for the scales and I've only scaled 3 times out of 30.

Um, yeah. :)

What I meant was, I've scaled a bunch of loads and also taken the pressure gauge readings on each axle for those same 100 loads. i.e 80 psi on the rear axle of trailer = 40,000 lbs. Then I made a chart using all these loads so whatever the psi is, we can get a pretty good idea what the axle weights are. If it's sitting level.