Each utility shall maintain the latest test records for each meter which shall include the following: The date and reason for the test; The reading of the meter before making any test; The proof “as found” at check flow; The proof “as left” at check and full rated flow; and If a test of the meter is made by using a working standard other than a bell prover, the utility shall retain all data taken at the time of the test in sufficiently complete form to permit the convenient checking of the test methods and the calculations.