Originally Posted by mtnguy
In that case, use a 3rd gauge. Still no guarantee, though.
You will then have 3 completely different readings (I actually tried this!)
I kept buying more expensive gauges to no avail. I now use the truck's on board air pressure system to "calibrate" the hand held unit I use to check the trailer tires.
I fill the truck tires until the DIC states 80 PSI, then let it sit a while and recheck to make sure it stays at 80. Put the gauge on and see what it reads. My gauge reads 4 PSI low at 80 PSI. So for the trailer tires (that I run at 55 PSI) I fill till the tires read 52 PSI. Using the "Rule of Thumb" that would be 3 PSI low at 55 PSI.