Shown here is a quick evolution of the Calibres 52 and 53, IWC's most common pocket watch movement. Almost 300,000 were produced from 1892 until 1940. You can read more about them on my IWC pocket watch website at click here.
The Calibre 52 (and its companion Savonette or "hunter) Calibre 53 evolved from IWC's rare Elgin III movements. Shown here at left is an Elgin III Calibre 48 from 1888, followed by a Calibre 50 from 1892 and, then at right, a Calibre 53 from the earlier 1900s. There are more similarities than differences as these movements evolved.
On the Calibre 48, you may notice the three-quarters plate with hidden winding wheels. The jewels, and the gear train, are in the same position as the later movements. The balance cock, lower left, has an nice elaborate engraving but a rudimentary regulator. As the movement evolved, the winding wheels are no longer hidden and there is a more complex regulator (at least in these latter two examples).
Also, as a minor point, note the shape of the three-quarters plate towards the bottom. On the Calibre 53 (and also on Calibre 52s) it is curved from side to side. On the earlier movements, it is straight along the balance cock and there is a semi-circle shape in the middle.
