No mystery to me since I have a couple good reference books and watch examples. migix is right. It is a very fine example of the best single button Lemania with unusual original black dial. Cannot see serial number but maybe 600+? This movement discontinued in 1935. A good guess for age 1933. Here serial 105.I don't think this is Lemania 13CH. It looks more like 15cht, but moreover it looks structurally identical to omega's 33.3. Actually, Lemania produced 33.3 for omega as a variation to 15cht, which was built into Tissot and Lemania at the time. Therefore, this particular watch is a mystery. Any other opinions?