settlement prices of the relevant December futures contract as traded on the  largest carbon market exchange (as determined by volume of sales of relevant  December futures contracts during the month) for each relevant day in the  month by the number of relevant days in the month;  (5) In this regulation—  “end of day settlement price”, in relation to the relevant December futures contract,  means the end of day settlement price per tonne of carbon dioxide equivalent published  by the carbon market exchange on which the relevant December futures contract is  traded expressed in pounds sterling or, where expressed in Euros, converted to pounds  sterling by reference to the Bank of England daily spot exchange rate for that day;  “EU emissions allowance” means an allowance to emit 1 tonne of carbon dioxide  equivalent during a specified period that is valid for the purposes of meeting the  requirements of Directive 2003/87/EC of the European Parliament and of the Council  of 13th October 2003 establishing a system for greenhouse gas emission allowance  trading within the Union( a ) and is transferable in accordance with the provisions of that  directive;  “relevant carbon market exchange”—  “relevant day” means a day for which an end of day settlement price is published;  “relevant December futures contract”, in relation to a day in the month referred to in  paragraph (4)(a) or the 24-month period referred to in paragraph (4)(b), means—  10. —(1) Regulation 16 is amended as follows.  (2) In paragraph (1)—  “(ba) investment firms which—  4 ( a ) OJ L 275, 25.10.2003, p. 32.  (a) after sub-paragraph (b), insert—  Regulation 16 (persons eligible to apply for admission to bid)  (d) if the day falls in December of 2021 or a subsequent year, a futures contract for  allowances deliverable in December of the year after the year in which the day  falls.”.  (c) if the day falls in January to November of 2021 or a subsequent year, a futures  contract for allowances deliverable in December of the year in which the day falls;  (b) if the day falls in December of 2019 or 2020, a futures contract for EU allowances  deliverable in December of the year after the year in which the day falls; (a) if the day falls in January to November of 2019 or 2020, a futures contract for EU  allowances deliverable in December of the year in which the day falls;  (b) in relation to the trading of the relevant December futures contract on a day in any  subsequent year (the “relevant year”), the largest carbon market exchange as  determined by volume of sales of relevant December futures contract during the  calendar year preceding the relevant year;  (a) in relation to the trading of the relevant December futures contract on a day in  2019, 2020 or 2021 means the carbon market exchange operated by ICE Futures  Europe (company no. 01528617);  (b) the “2-year average carbon price” must be calculated by dividing the sum of the  end of day settlement prices of the relevant December futures contract as traded on  the relevant carbon market exchange for each relevant day in the 24 months ending  with the last month before the first month of the period of 3 or, as the case may be,  6 months referred to in paragraph (3) by the number of relevant days in the 24- month period.