(1)This section applies for the purposes of section 656.
(2)“Exactly tracking contract” means a contract where the amount which is to be paid to discharge the rights and liabilities which fall to be treated as comprised in the contract is equal to the amount found by applying R% to C, where—
R% is the percentage change (if any) over the relevant period in—
(a) the value of the assets which are the underlying subject matter of the contract, or
(b) any index of the value of those assets, and
C is the amount falling to be regarded in accordance with generally accepted accounting practice as the proceeds of issue of the liability which represents the debtor relationship mentioned in section 656(2).
(3)In subsection (2) “the relevant period” means—
(a)the period between—
(i)the date when the liability representing that debtor relationship came into existence, and
(ii)the date when the creditor relationship corresponding to that debtor relationship comes to an end, or
(b)any other period in which almost all of that period falls, and which differs from that period only for purposes connected with giving effect to a valuation in relation to rights or liabilities under the liability representing that debtor relationship.