“nominated date”, in relation to a display energy certificate, means a date no later than three months after the end of the period over which the operational rating is calculated, which is nominated by the energy assessor who issued the certificate; and

“operational rating” means a numeric indicator of the amount of energy consumed during the occupation of the building over a period of 12 months (unless regulation 18(4) applies) ending no earlier than three months before the nominated date, calculated according to the methodology approved by the Secretary of State for the purposes of regulation 17A of the Building Regulations 2000.