26 U.S.C. § 7517: Furnishing on request of statement explaining estate or gift valuation

If the Secretary makes a determination or a proposed determination of the value of an item of property for purposes of the tax imposed under chapter 11, 12, or 13, he shall furnish, on the written request of the executor, donor, or the person required to make the return of the tax imposed by chapter 13 (as the case may be), to such executor, donor, or person a written statement containing the material required by subsection (b). Such statement shall be furnished not later than 45 days after the later of the date of such request or the date of such determination or proposed determination. explain the basis on which the valuation was determined or proposed, set forth any computation used in arriving at such value, and contain a copy of any expert appraisal made by or for the Secretary. Except to the extent otherwise provided by law, the value determined or proposed by the Secretary with respect to which a statement is furnished under this section, and the method used in arriving at such value, shall not be binding on the Secretary. insofar as they relate to the tax imposed under chapter 11 of the Internal Revenue Code of 1986 [formerly I.R.C. 1954, section 2001 et seq. of this title], shall apply to the estates of decedents dying after December 31, 1976 , and insofar as they relate to the tax imposed under chapter 12 of such Code [section 2501 et seq. of this title], shall apply to gifts made after December 31, 1976 .”