The ETA caliber 2893-2 is part of the Mecaline Specialities line of ETA movements. This caliber can be supplied by ETA with a Chronometer rating. The 2893-2 is very similar to the ETA 2892-A2 except that it has a GMT complication. The example in the photos is from a Sinn 857 S UTC.
The GMT hand sets independently. Unscrew crown and pull to position I, turning forward/clockwise will adjust the GMT hand by one hour increments. Turning the crown backwards/counter-clockwise will adjust the date. This is very convenient because you can adjust the GMT hand without hacking (stopping) the movement. For GMTs that require hacking the movement to adjust the GMT hand, it also requires readjusting the time.