When using the direct comparison method to calibrate instruments, how should a standard gauge be selected?

When using the direct comparison method to calibrate instruments, a standard gauge with high precision should be selected

The measurement error of the standard gauge is about 1/3 of the indicated error of the gauge being calibrated.

When the comparison environments are the same, of course one chooses the one with high precision and a low price.

The accuracy of the standard gauge is 1/3 or less of the accuracy of the gauge being calibrated; for example, when calibrating a pressure gauge of grade 1.6, the standard gauge used should be at least grade 0.5

There are three principles for selecting a standard table: First, based on the nature of the table to be calibrated. For example, if the meter to be calibrated is a DC voltmeter, then the standard meter selected should also be a DC voltmeter ； Second, based on the rated value of the table being calibrated. The rated value of the standard gauge shall be compatible with that of the gauge being calibrated, or shall not exceed 25% of the rated value of the gauge being calibrated. For example, if the range of the gauge to be calibrated is 2000 kPa, then a standard gauge with a range of 2500 kPa should be selected ； Third, it is necessary to consider the accuracy of the table being calibrated. The allowable error of the standard gauge should not exceed 1/3 of the allowable error of the gauge being calibrated. If the accuracy of the watch to be calibrated is grade 1.5, the accuracy of the standard watch should be grade 0.5.