19.—(1) Subject to sub-paragraph (2), measurements may be performed by means of any relevant instrument provided that the temperature range to which a relevant instrument is exposed is not wider than the range specified by the manufacturer in relation to that relevant instrument in accordance with paragraph 3(1)(a) and Table 1 of this Schedule.
(2) Class A relevant instruments may not be used when operating outside the temperature range of an upper temperature limit of 30 °C to a lower temperature limit of 5 °C.
(3) The person responsible for installing the relevant instrument shall determine the correct current range and assess the climatic environment, so that the relevant instrument is appropriate for the accurate measurement of consumption that is foreseen or foreseeable.