This was my grandfathers calculator, which he used for some business calculations (he was a "master ('Meister') craftsman" painter in East Germany, responsible

This was my grandfathers calculator, which he used for some business calculations (he was a "master ('Meister') craftsman" painter in East Germany, responsible for a team) into the 1990s even after he already had an electronic calculator. https://i.imgur.com/jBDUHPp.jpeg https://i.imgur.com/jBDUHPp.jpeg Does anybody have any information about this machine? I used to be able to do simple calculations with it, but nowadays I don't remember anything at all. I guess using trial and error I might be able to do additions and multiplications, but I would not be able to use even a fraction of that machine's capabilities. Sadly, there's no (surviving?) handbook.