Use of Tolerances. All tolerances are to be interpreted as maximum permissible variation from the condition of zero error. In making adjustments, no advantage of the prescribed tolerance limits may be taken to set meters fast. Reading and Recording Data. Maximum Readability. In any test or calibration, the devices or instruments used in the test or calibration shall be read to the maximum degree of readability. Degree of Accuracy. The degree of accuracy achieved in the calculations involved in determining the accuracy of a meter, prover, device, or instrument in any test or calibration shall be consistent with the purpose for which the resultant accuracy is to be used. Recording. The final accuracy or proof shall be recorded to the nearest 0.5 percent. Overall Accuracies. The overall accuracy or proof of a meter and an associated device, which affects the meter readings for billing purposes, may not be more than 0.5 percent fast or more than 1.5 percent slow. Diaphragm Type Meters. Diaphragm meters may not be placed or left in service unless found upon test to comply with the following: The meter may not be more than 0.5 percent fast nor more than 1.5 percent slow at check flow or at full rated flow. The proof at full rated flow may not differ from the proof at check flow by more than 1 percent. When air is used for testing meters, the rate of flow shall be adjusted to compensate for the difference in the specific gravity of air and the specific gravity of gas. Rotary Type Meters. Rotary type meters shall be tested at not less than 15 percent of full rated flow. A utility may not install a rotary meter which is more than 0.5 percent fast or more than 1.5 percent slow at the points of test. Turbine Type Meters. Turbine type meters shall be tested at not less than 15 percent of full rated flow. The meters may not be more than 0.5 percent fast or more than 1.5 percent slow at the points of test. Pressure Correcting Devices. Pressure correcting devices may not be more than 0.5 percent fast or more than 1.5 percent slow in the pressure range for which the instrument is intended to be used. Temperature Correcting Devices. Temperature correcting devices may not be more than 0.5 percent fast or more than 1.5 percent slow at the points at which they are tested. Timing Devices. Timing devices may not have an error more than 0.25 percent.