40 CFR 91.305 - Dynamometer specifications and calibration accuracy.
(a) Dynamometer specifications. (1) The dynamometer test stand and other instruments for measurement of engine speed and torque must meet the accuracy requirements shown in Table 2 in appendix A to this subpart. The dynamometer must be capable of performing the test cycle described in § 91.410.
(b) Dynamometer calibration accuracy. (1) The dynamometer test stand and other instruments for measurement of engine torque and speed must meet the calibration frequency shown in Table 2 in appendix to this subpart.
(2) A minimum of three calibration weights for each range used is required. The weights must be equally spaced and traceable to within 0.5 percent of National Institute of Standards and Testing (NIST) weights. Laboratories located in foreign countries may certify calibration weights to local government bureau standards.