The period of ten years specified in section three of the [26 Geo. 5. & 1 Edw. 8. c. 20.] Electricity Supply (Meters) Act, 1936, (which provides that certain meters shall be deemed to be proper meters for ascertaining the value of a supply), being the period after which that section is to cease to apply to any meters, shall be extended by a further period of five years, and accordingly for the words " ten years " in subsection (3) of that section there shall be substituted the words " fifteen years ".