17 C.F.R. § 270.2a-4
(a) The current net asset value of any redeemable security issued by a registered investment company used in computing periodically the current price for the purpose of distribution, redemption, and repurchase means an amount which reflects calculations, whether or not recorded in the books of account, made substantially in accordance with the following, with estimates used where necessary or appropriate.
(c) Notwithstanding the requirements of paragraph (a) of this section, any interim determination of current net asset value between calculations made as of the close of the New York Stock Exchange on the preceding business day and the current business day may be estimated so as to reflect any change in current net asset value since the closing calculation on the preceding business day.
(Secs. 7, 19(a), 48 Stat. 78, 85, 908, 15 U.S.C. 77g, 77s(a); secs. 12, 13, 15(d), 23(a), 48 Stat. 892, 894, 895, 901; secs. 3, 8, 49 Stat. 1377, 1379, secs. 3, 4, 78 Stat. 569, 570, secs. 1, 2, 82 Stat. 454, 15 U.S.C. 78l, 78m, 78o(d), 78w(a); secs. 8, 22, 30, 31(c), 38(a), 54 Stat. 803, 823, 836, 838, 841, 15 U.S.C. 80a-8, 80a-22, 80a-29, 80a-30(c))
[29 FR 19101, Dec. 30, 1964, as amended at 35 FR 314, Jan. 8, 1970; 47 FR 56844, Dec. 21, 1982]