presumed markup percentage
(3) Long-term lease (A) In general In the case of any long-term lease of an article which is treated as the first retail sale of such article, the tax under this subchapter shall be computed on a price equal to— (i) the sum of— (I) the price (determined under this subchapter but without regard to paragraph (4)) at which such article was sold to the lessor, and (II) the cost of any parts and accessories installed by the lessor on such article before the first use by the lessee or leased in connection with such long-term lease, plus (ii) an amount equal to the presumed markup percentage of the sum described in clause (i). (B) Presumed markup percentage For purposes of subparagraph (A), the term “presumed markup percentage” means the average markup percentage of retailers of articles of the type involved, as determined by the Secretary. (C) Exceptions under regulations To the extent provided in regulations prescribed by the Secretary, subparagraph (A) shall not apply to specified types of leases where its application is not necessary to carry out the purposes of this subsection.
26 USC § 4052(b)(3)
None identified, default scope is assumed to be the parent (subchapter C) of this section.