|(a) This rule applies only to motor fuel transactions that take place on or after January 1, 2004. Motor fuel transactions that occur prior to January 1, 2004, will be governed by sections in Texas Administrative Code, Title 34, Part 1, Chapter 3, Subchapter L. The words and terms used in this section have the same meaning as those defined in Tax Code, Chapter 162. (b) Metering devices. A metering device that complies with the specifications set out in subsection (c) of this section may be used as a basis for determining the quantity of gasoline consumed in the operation of an auxiliary power unit or power take-off equipment mounted on a motor vehicle. (c) Design specifications. The meters shall be designed to separately measure the fuel used by the motor vehicle from the fuel used to operate the power take-off or the auxiliary power unit. (1) The metering device, or a model thereof, must be tested for accuracy and proper performance by the Texas Engineering Experiment Station, Texas A&M University, or other testing agency approved by the comptroller. The test must clearly establish that the metering device operates within the acceptance tolerances for allowable error or departure from true performance set forth in the National Bureau of Standards, U.S. Department of Commerce Handbook 44, latest edition for slow-flow meters; (2) The metering device must be designed so that the gasoline will flow through and be recorded by the metering device only when the motor vehicle's spring-loaded air-parking brake or other approved air-parking brake, or hydraulic parking brake is engaged, or when any hydraulic power take-off unit that can be operated only when the motor vehicle is stationary and the hydraulic power take-off unit is engaged. The device must be designed so that gasoline will at all times flow through a by-pass line when the air brakes, hydraulic brakes, or hydraulic power take-off units described above are disengaged, or when the motor vehicle is not stationary. (3) The metering device installed on the motor vehicle must be maintained in a manner in which the device will operate at all times within the maintenance tolerances set forth in Handbook 44 for slow-flow meters. (d) Disallowance of tax credit or refunds. It is expressly provided that tax credits or tax refunds may be disallowed for tax paid on gasoline that was measured and recorded by any metering device that is not maintained as required by subsection (c) of this section or when the owner or operator fails to keep the following records for at least four years: (1) a complete record of the total miles traveled by each motor vehicle equipped with such metering device as shown by the speedometer, odometer, or hubmeter readings accurately maintained; (2) the total gallons of gasoline delivered into the fuel supply tank of each vehicle equipped with such metering device as shown on purchase invoices or a distribution log; and (3) each claim for tax credit or tax refund shall be supported by such mileage and fuel consumption records and a record of the beginning and ending meter readings recorded on such metering device for each refund period.