See Acid number for Test Method D 664 that follows. Oils such as many cutting oils, rustproofing oils, and similar compounded oils, or excessively dark-colored oils, that cannot be analyzed by this test method due to obscurity of the colorindicator end point, can be analyzed by Test Method D 664. The acid numbers obtained by this color-indicator test method may or may not be numerically the same as those obtained by Test Method D 664.