Hi Gene, The film speed value assigns a numeric value number to the sensitivity of a photographic material. Methods and tests to establish this value started with Messrs.Hurter and Driffield, two British amateur photographers who together founded the science of Sensitomerty / Densitometry in 1890. At that time, film speed was known as H&D speed. In the 1930’s Kodak Lab’s Loyd Jones and co-workers refined this science. The American Standards Association adopted the Kodak method in 1960. The International Standards Organization adopted the ASA method and then made refinements. While there are minor differences they are not significant and ISO remains the benchmark method. Over the years, other methods were developed by light meter makers, General Electric and Weston, whoo independently established film speeds. So too did the European film makers who created a system known as the DIN for Deutsche Industrial Norm. Not to be outdone, the British established BAS using ASA methods. The Russians chimed in with GOST. Only ISO survived. Alan Marcus (marginal technical gobbledygook) Anaheim, CA ammarcus@earthlink.net

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