3(1)For the purposes of subsection (5) of section 2 of this Act the aggregate market value of any oil falling within paragraph (b) or (c) of that subsection shall be arrived at by ascertaining, for each calendar month in the chargeable period in question, the market value at the material time of so much, if any, of that oil as was—
(a)in the case of oil falling within the said paragraph (b), delivered as there mentioned in that month; or
(b)in the case of oil falling within the said paragraph (c), appropriated as there mentioned in that month,
and, in either case, aggregating the market values so ascertained.
(2)In this paragraph and elsewhere in this Part of this Act " calendar month" (where those words are used) means a month of the calendar year, and " the material time", in relation to a calendar month, means noon on the relevant day, that is to say—
(a)for a month containing an odd number of days, the middle day of the month ;
(b)for a month containing an even number of days, the last day of the first half of the month.