It's been my experience (limited) that guages are nonlinear beasts and are calibrated to be most accurate @ 20% (400 psi here) and 80% (1600 psi). If they read accurate at 0 and full scale, well, that's just gravy.
Is that the guage for tank pressure? If no, you need a different guage.
If so, is the tank valve open feeding gas to the reg.? If closed I wouldn't care as long as it seems to read correctly when gas pressure is applied.
Is this a rebuilt or costom built reg? The guages seem to be wrong based on mine. A pic of the other guage would be nice. And a little more info on why you are asking could help.
Gotta go to the plant floor now. Be back when I can.