Calibration of test equipment. All shop and portable instruments used for testing billing submeters shall be calibrated by comparing them with a reference standard atleast every 120 days during the time such test instruments are being regularly used. Test equipment shall at all times be accompanied by a certified calibration card signed by the proper authority, giving the date when it was last certified andadjusted. Records of certifications and calibrations shall be kept on file in the officeof the owner.
Calibration of test equipment. Test equipment is calibrated, if required, periodically on the basis of stability, purpose, and degree of use. The equipment is calibrated by an outside laboratory and is traceable to N.B.S. standards.
