Pressure gauge calibration can be performed using a variety of methods, such as using a hydraulic test pump (with suitable and accurate reference gauges) or a pressure piston weight tester. Whichever option you choose, it should be performed by an experienced professional using high-quality, certified calibration equipment.

Using a suitable pressure medium (gas or liquid), the test pump simultaneously pressurises the pressure gauge under test and the digital reference pressure gauge from inlet ports on both sides of the pump. Then compare both readings to identify discrepancies. 

A pressure balance is used for comparing a pressure gauge against a set of weights, which takes into account many factors such as gravity, buoyancy, and revolutions per second, compares the gauge under test to a set of weights, but this type of calibration is often performed on a pressure gauge - where you need more precision.

Regardless of the calibration method used, if the deviation is greater than the defined tolerance, the pressure gauge should be adjusted and recalibrated or taken out of service.