This heavy duty service gauge is calibrated to 150 PSI in 2 PSI increments making it accurate to within 2 PSI.
Both gauges work straight onto the valve stem and at an angle for the outside dual. The 180 degree reverse works on aluminum wheels where the outside dual valve stem points into the hand hole at a 180 degree angle. The 30 degree reverse works on steel wheels where the outside dual valve stem points into the hole at a 30 degree angle.
A service gauge will stay accurate longer if you store it in a long sock to keep the dust out of the stick and place it where it won’t get knocked around. The ring on the side comes in handy if you have a place to hang it.