The proper procedures, correct methods and rules for rounding-off are presented in this paper for the reading of the test data of general pressure gauges and tyre pressure gauges. The method for rounding off the allowable errors of pressure gauges is introduced. The correct reading method for tapping displacement and return errors of pressure gauges is pointed out. Analysis is made on the quick determination method for deciding whether the pressure value errors are exceeding the allowable errors. The correct method for determining the deflection of the pressure gauge pointer is pointed out.