The sensitometry chapter in Haist includes a good summary of ANSI formulas and procedures for determining the speeds of various photographic materials. Interestingly, the developer composition specified in PH2.5-1972 is identical to the one in PH2.5-1979 except for a weaker carbonate alkali system: 1.5g Sodium carbonate (anhydrous) and 1.0g Sodium bicarbonate, with a specified pH of 9.4 +/- 0.2. I wonder why the change was made in 1979 and how the composition was determined.