Hello,
in the 1940- and the beginning -50-years it was usual to use the old unit system wit cm instead of mm (the German 8.8Flak also had a caliber of 8.8 cm, not 88 mm). I cannot say when Leitz did change from cm to mm, I have a 5 cm Summarit, a 5 cm fixed Summicron an a 2.8/50 mm E 39 Elmar. The distance scale could be only in meter or only in feet or lateron both.