Dating gruen watches
By the time the Bestfit and other similar movement identification books were introduced, which seems to have begun in the 1940s, most of the watches current at that time had cover plates with integral detent springs.The fingerprints in the Bestfit book can be used to easily identify these movements.However, to see the keyless work requires the dial to be removed, which may not be possible, and many older movements are not documented in these references.The pictures on this page can help to identify movements without seeing the keyless work, but be careful to make sure that all the features, the shapes of the plates and bridges, the placement of the screws and pivots, are exactly the same; similar is not close enough!If you click on the pictures a bigger one should pop up in a new window.I don't mind you using these for your own personal research, but if you want to use them elsewhere such as on an internet forum, a web site, or in a publication, please read my copyright notice first and include attribution.Stem set keyless work needs a detent to hold the crown in the winding or setting position.
Manufacturers altered the appearance of their movements by changing the top plates, but the basic layout remained much the same.
For example, The Bestfit Book includes the diagram shown here of the parts of the keyless work of ETA calibre 715 and Eterna 710.
The most significant part for identification is the largest part, the cover plate.
Movements from the 1920s or earlier, with cover plates that don't have integrated detent springs, don't generally appear in the Bestfit or similar books and are therefore harder to identify. The first step in identifying a movement is to determine its size in lignes.
The cover plates are often just as unique, it's just that by the time the Bestfit books were introduced, watches with such movements were considered "obsolete". The image here from the "Official Catalogue of Swiss Watch Repair Parts" issued by the Watchmakers of Switzerland in 1948 shows how movements are measured for diameter D and height H.