American Society for Testing and Materials (ASTM). Current edition approved June 1, 2010. Published November 2010. Originally approved in 1989. Last previous edition approved in 2004 as E 1311 – 89 (2004). 1 p. This test method covers the determination of the minimum detectable temperature difference (MDTD) capability of a compound observer-thermal imaging system as a function of the angle subtended by the target.