For the 507 and 507RV-Flow Thru units, TST claims 1.5psig accuracy in their current manuals. Mine are in the 2-3 pound low range. This doesn't bother me if they are not consistent with a spec and I know where I started (80 psig in my LT tires on our 5er set by a good gauge). I also look at temperature rise from starting ambient vs the gauge on my TV's dash and the external temp on the digital thermometer in the RV. Again, if we haven't moved yet, that temp and pressure reading can be different from side to side depending on how long the sun has been 'beating' on the tire. After all that, I'm more concerned with sudden high or low delta T and/or P after driving a distance rather then an absolute. These inexpensive measuring gadgets - and they really are - just are not capable of those kinds of tight parameters.
Know what your tire pressure is when you start as well as temps then look for sudden changes either up or down is really about all the real
information these TPMS can tell you regardless of advertising.
: My opinion and how I use my TST unit, others may and will have theirs