The standard instrument for calibrating pressure gauge is 

A dead weight tester is the standard instrument used for calibrating pressure gauges. It works by applying a known pressure to the gauge under test using calibrated weights. The pressure is generated by the weights acting on a piston or piston-cylinder assembly, creating a force that is directly proportional to the pressure being measured. This allows for accurate calibration of the pressure gauge. Oscilloscopes are used for measuring and analyzing electrical waveforms, while dry block temperature testers are used for calibrating temperature sensors. Dry weight testers are not a recognized instrument for calibrating pressure gauges.