18.—(1) Measurement of residential use shall be performed by means of any Class 1.5 relevant instrument, or by Class 1.0 relevant instruments which have a Qmax/Qmin ratio equal or greater than 150.
(2) Measurement of commercial and/or light industrial use shall be performed by any Class 1.0 or Class 1.5 relevant instrument.
(3) The person responsible for installing a relevant instrument shall have regard to the requirements under paragraph 12(b) and (c) and shall ensure that the relevant instrument is appropriate for the accurate measurement of consumption that is foreseen or foreseeable.