Film speed
As in the Scheiner system, speeds were expressed in 'degrees'. Originally the sensitivity was written as a fraction with 'tenths' (for example "18/10deg DIN"), where the resultant value 1.8 represented the relative base 10 logarithm of the speed. 'Tenths' were later abandoned with DIN 4512:1957-11, and the example above would be written as "18deg DIN". The degree symbol was finally dropped with DIN 4512:1961-10. This revision also saw significant changes in the definition of film speeds in order to accommodate then-recent changes in the American ASA PH2.5-1960 standard, so that film speeds of black-and-white negative film effectively would become doubled, that is, a film previously marked as "18deg DIN" would now be labeled as "21 DIN" without emulsion changes.
When did the degree symbol fall out of use in the DIN system?
with DIN 4512:1961-10
The degree symbol was finally dropped with DIN 4512:1961-10.
the degree symbol