Michigan Compiled Laws, Chapter 290. Weights, Measures and Standards § 290.628d

Sec. 28d. (1) Notwithstanding any requirements adopted under section 28c,  1 the gross weight of a vehicle shall be determined by weighing the vehicle in a single measurement for a vehicle that is not a tractor-trailer combination and not by adding the results of multiple measurements taken at opposite ends of the vehicle. The gross weight of any tractor-trailer combination shall be determined by the method described in subsection (2).

(2) The gross weight combination of a truck tractor with multiple trailers shall be determined without uncoupling and by using a method of split weighing and combining the measurements, if necessary, if the following conditions are met:

(3) A scale used to weigh vehicles under subsection (2) shall be tested at least annually or upon repair or maintenance of the weights and measures device, by weighing a coupled tractor with multiple trailers as a single unit and comparing that weight with the combined weight of each vehicle weighed separately. If the weights determined by this method vary by more than 0.2%, the scale shall not be used to determine the gross weight of vehicles while they are coupled until the scales are corrected to properly measure within the 0.2% range.All testing data shall be recorded and the records retained on site by the owner or operator and made available to the department for review upon request.

(4) If a scale cannot be used to weigh vehicles under subsection (2) while they are coupled, the vehicles shall be weighed individually and the weights totaled to obtain the gross weight of the vehicle combination.

(5) This section does not apply to the enforcement of vehicle weight under the Michigan vehicle code, 1949 PA 300, MCL 257.1 to 257.923.