From Chinese Watch Wiki
The ST21 is an automatic, 26 jewel, 28,800 bph watch movement manufactured by Tianjin Seagull. The design is essentially a clone of ETA's 2824 movement. A slightly more generous description is that it is a "re-engineered version of the ETA 2824-2", with "unnecessary, wasteful and difficult processes .. removed".
- Watchuseek forum thread: How do Seagull and Hangzhou compare to a ETA: An in-depth look... (ST2130 and HZ6300 tear down)
- Watchtalk forum thread: Seagull ST2130 disassembly