5. Where the measurement method with the engine at a constant speed or the measurement method with the engine at a variable speed is applied, the rotational speed of the engine must be verified with an external tachometer that complies with the requirements described in paragraph 3 of section 9. If it is impossible to use an external tachometer, in particular because the environment or configuration of the vehicle does not allow it, the tachometer of the vehicle may be used.
588-2019O.C. 588-2019, s. 5.