19(1)A person's entitlement to relief under this Schedule for a trade in respect of a period of account shall be determined in accordance with this paragraph if the trade is set up and commenced at the beginning of that period or in the course of it
(2)The relief to which the person is entitled for the trade in respect of the period of account shall be determined—
(a)as if the value of his trading stock at the end of that period, as reduced in accordance with sub-paragraph (3) below, were the value of his trading stock at the end of the preceding period of account; and
(b)if the period of account begins before the date on which the trade is set up and commenced, by reference to the increase, if any, in the all stocks index over the part of that period beginning with that date.
(3)For the purposes of sub-paragraph (2)(a) above the value of the person's trading stock at the end of the period of account in respect of which the relief is given shall be reduced by multiplying it by the fraction of which—
(a)the numerator is the figure given by the all stocks index for the month containing the last day before the beginning of that period; and
(b)the denominator is the figure given by that index for the month containing the last day of that period.
(4)If the period of account begins before the date on which the trade is set up and commenced the reference in sub-paragraph (3)(a) above to that period of account shall be construed as a reference to the part of it beginning with that date.
(5)Sub-paragraph (2) has effect subject to paragraph 23 below.