For many years, Sellita operated as one of ETA’s major out-sourced assembly operations for their 2824 movements.
They would receive 2824 movement kits from ETA and assortments from Nivarox directly (now part of the Swatch Group) and simply add wheels and screws and sell the movements to many famous Swiss watch brands as ETA 2824-2 movements, which in effect they were.
When it was announced that ETA would no longer be providing unfinished movement kits, this threatened Sellita’s survival as a business. Their solution was to buy the parts from suppliers outside the Swatch Group with the exception of Nivarox who, as a result of the long-standing relationship over 50 years, they continued to use. At first, they weren’t sure if they would have IP issues if they copied the movement exactly so they re-engineered the movement, changing some minor details These changes, although minor, added up to reduced reliability in the pre-series movements and so, Sellita decided (having now learned that there were no remaining patents for the 2824) to return almost entirely to the ETA movement design.
We started to use Sellita’s SW200 ( the name for Sellita’s 2824-2) at this point and, having checked the performance of each subsequent delivery of both movements, we are able to confirm the movement performance exactly matches the ETA.
Aesthetically, the movements are identical and difficult to separate and the only significant difference is in the number of jewels. Sellita added a 26th jewel on the upper side of the barrel axis which sits just below the ratchet wheel. This jewel slightly reduces the friction associated with automatic winding. However, as the ETA movement has never had a problem of reliability in this regard, it is my view that this is most likely a marketing device used by Sellita to create some separation from the ETA movement although one could make a case for the small benefit in reliability the adjusted jewel height gives.
Overall, however, the two movements are so identical in every aspect, it is difficult to have a meaningful discussion about the differences.