(a) Variable finance charge percentage rate.--Notwithstanding any provision of law to the contrary, the finance charge percentage rate included in an installment sale contract for the sale of a heavy commercial motor vehicle may vary during the term of the contract pursuant to a formula or index set forth in the contract that is made readily available to and verifiable by the buyer and beyond the control of the holder of the contract.
(b) Determinations.--Notwithstanding that the finance charge percentage rate may increase or decrease over the term of the contract according to a formula or index set forth in the contract, the rate applicable to the transaction as of the date of execution of the contract may be used to determine the following:
(1) The amount of finance charge under section 6222(5)(vii) (relating to contents).
(2) The time balance under section 6222(5)(viii).
(3) The payment schedule under section 6222(5)(ix).