There are also "C" and "D" grade gauges, which are 4% and 5% respectively.
If you have a 0-50 psi "D" grade gauge, it should read accurate +/- 2.5 psi. A 0-15 psi "D" grade gauge will read accurate +/- 0.75 psi.
A "graded" gauge means that it has been tested and it complies with ASME specifications.
A non-graded gauge, well, the manufacturer may have built it to certain specifications, but they cant really tell you if it is accurate. They may do random testing, but how big is the lot size between tests? How many lemons are getting shipped out? I've had lemons in the past and it cost me on one project! Never used a non-graded gauge since then!
If you put a flowmeter on your rig, put the gauge "after" the flowmeter. If you have a lot of hardware like manifolds, valves... I would put one at the pump and one on the line out to the fuser. It will give you an idea of what your pressure drop across these items is. It may be really low, or could be significant.
