This camera was mainly intended for use by amateur photographers who only occasionally used the camera. Film was loaded, some pictures taken, the camera was generally set-aside to be picked up latter for an occasion. This second or perhaps third session might be next week or next month or even next year. When the roll was finished, then it was sent out to the photofinisher for developing and printing.
What I what you to understand, it was common for the loaded camera to sit in a drawer for some time. Naturally, one tended to forget what type of film was loaded.
The letters and numbers on the wheel you have discovered is a reminder. The letters stand for film types. The lettering, in in English was CT for color transparency (slide film) -- CN for color negative film, B or BK for black & white.
In that era, film speed testing was carried out by the various standards bureaus of counties. In North America it was ASA (American Standards Association). In Germany it was DIN (Deutsche Industrial Norm), BSI (British Standards Institute), in Russia GOST etc. Each used different methods, it was confusing, all were consolidated under the authority of the International Organization for Standardization of Geneva and now called ISO.
The DIN system of Europe was Logarithmic. 100 ISO = 21⁰ -- 200 ISO = 24⁰ -- 400 ISO = 27⁰ (approximate conversion.
However, the wheel was a reminder device, it is not connected to the camera’s mechanism, it serves only to remind the photographer what film was inside.