- Another example of a good collectible is finding an early application of a stem winding M57 where the stem cannot be turned backwards and movement is key set. I'm still looking (slide 11 is not my watch - WWCo 597388).
- There are a lot of stem wind M57s, and many look junky, but which grade and serial number range would have this (lack of) feature.
- See paper and Additional Notes section of the tables. WWCo grade S/Ns 555,501-610 & 597,000-597,500 are good candidates.