I have a feeling the one on my pump isn't the most accurate there is. In fact, most bike and auto tire pressure gauges seem to have some notoriety in being inaccurate.
Can anyone recommend an accurate, reliable and inexpensive pressure gauge?
if your using a road bike, tire pressure on road bike goes upo as high as 120psi, but on MTB maybe 50-60psi, I will not be able to recommend any tire pressure guage, but I am using Silca floor pump and it has an air pressure guage and I foind that they are almost close to the accurate thing, so hand held air pressure guages, can't exactly give you the result you want, You might try using this floor pump with the guage..
Most floor pumps have a fairly accurate pressuge gauge mounted on the front. That's what I use.
If I have a flat or slow leak while out riding, I pump up the tire with the frame pump and do the "feel" test. If it feels about as firm as when pumped up by the floor pump I'm happy.
I bought one of these at my LBS years ago. It was not expensive. It is dependable and, as far as I can tell, accurate.
REI has them for $11.00