(a) Location. Air gauges shall be so located that they may be conveniently read by the engineer from his or her usual position in the cab. No air gauge may be more than 3 psi in error.

(b) Frequency of testing. Air gauges shall be tested prior to reapplication following removal, as well as during the 92 service day inspection and whenever any irregularity is reported.

(c) Method of testing. Air gauges shall be tested using an accurate test gauge or dead weight tester designed for this purpose.