19.—(1) The measurements and calculations required by this Chapter, or necessary for demonstrating or measuring conformity with this Chapter, must be made in accordance with designated standards, where available.
(2) Where designated standards are not available, the measurements and calculations referred to in paragraph (1) must be made in accordance with methods which —
(a)can be demonstrated to be reliable, accurate, and reproducible by the person deploying them; and
(b)take into account the generally recognised state of the art.