Sellita Cal. SW501 M MP b is a hand-winding monopusher chronograph movement in the Sellita SW500 family. It is based on the ETA 7750 design and shares many components with that movement. Sellita introduced the monopusher MP function in 2018 along with the hand-winding version of the SW500 line. All hand-winding SW500 M movements feature a special bridge with larger jewels and a cut-out to allow the cam-switching chronograph function to be visible through a display caseback.
This movement features a single button at 2:00 for chronograph start/stop/reset. It has running small seconds at 9:00, a date window at 3:00, and a 15 minute chronograph counter at 12:00.
Sellita SW500 and SW600 Technical Information
The Sellita SW500 and SW600 movements are based on the Valjoux 7750 design, itself based on the Valjoux 7733 and Venus 188. This movement is known for durability and flexibility and is used as a base in many watches, from entry-level chronographs to the famous IWC “Il Destriero Scafusia” grande complication. It is a large and relatively thick movement, measuring 13.25 ligne (30.00 mm) in diameter and 7.90 mm thick.
Although based on a classic design, the modern SW500 and SW600 is robust and full-featured. It operates at 4 Hz (28,800 A/h) with an efficient uni-directional central winding rotor. The day and date wheels feature crown-operated quick correction and a stop seconds (“hacking”) feature is included. The base movement has the famous Valjoux 6-9-12 subdial layout with small seconds at 9:00, but many Sellita versions have other subdial designs.
One major differentiator for the Sellita movements is the use of an eccentric screw for regulation rather than the traditional Valjoux articulated index.
Sellita 500 M MP Variants
| Date at 6:00 Chonograph Minutes at 12:00 | Date at 3:00 Chronograph Minutes at 12:00 Small Seconds at 9:00 | Date at 3:00 Small Seconds at 9:00 | |
|---|---|---|---|
 |  |  | |
| No Chronograph Counters | SW500 M MP c | ||
| 30 Minute Counter | SW500 M MP a | SW500 M MP b | |
| 15 Minute Counter | SW501 M MP a | SW501 M MP b |
