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If you use an old film camera you may have noticed there's a dial with the abbreviations ASA and right next to it DIN. You likely have already figured out to use ASA where your film says ISO. ISO and ASA are interchangeable. From prehistoric times (ok, since the middle of the 20th century) to the late 1980's ASA was what much of the world used as measure of film sensitivity. The abbreviation stood for American Standards Association. At the same time, the German version of the organization that measured film sensitivity was abbreviated DIN or Deutsches Institut für Normung meaning German institute for Standards. Germany was and to some degree still is an influential player in photographic innovation and manufacture.  DIN wasn't a linear measure. Doubling of sensitivity was shown by adding 3 to the number. For example 21 DIN (=100 ASA/ISO) and 24 DIN (=200 ASA/ISO.) DIN and ASA ISO are equal at 12. So: ISO 12 = DIN 12  ISO 25 = DIN 15 ISO 50 = DIN 18 ISO 10

Here's a sheet I got from writing ORWO Technischer Kundendienst back in the 1980's. It lists development times for all the ORWO Black and White films sold for export at the time (NP15, NP22, NP 27) combined with western developers Microphen, Atomal, Rodinal, Refinal, D-76, & ID-11. A little bit of ORWO history- Germany's big photo film/paper manufacturer up until Germany's losing WWII was AGFA (short for  A ktien G esellschaft F ür A nilinfabrikation - or corporation for some sort of plastic manufacture.) Germany was occupied by the winning powers USSR/USA/GB/FR and the rift between the USSR led to some complications for industries. Depending on your view of history the US and western allies were much friendlier to the land they occupied (remember the USSR lost many millions of their citizens to the NAZIs which made them much less tolerant.) In any case, some factories in the east moved to the west with many key employees. Most photo enthusiasts know of the t