Once upon a time Tudor used Rolex cases but differed from their sibling brand by using generic ETA movements (2873, 2824), later modifying these with its own balance shock, regulator, and a movement finishing (pearlage). This was the case until recently (2015), when Tudor created its own in house movement the COSC capable Tudor calibre MT5612 and MT5621.
The MT5612 base movement is a 26 jewel 4Hz nickle plated movement with a minimal Côtes de Genève finishing. The MT5621 has 28 jewels and differs only in that it features a power reserve complication where as the 26 jewel MT5612 does not. It is also the first movement in the brands history to ever be submitted for COSC certification, something every modern Rolex undergoes, and that means it should preform within a -4/+6 daily accuracy (Tudor proudly claims their movements actually exceed this standard at -2/+4 on average).
Currently this movement is only available in the COSC version of the Tudor Pelagos (25600T N/B MT5612) and the Tudor Northflag (MT5621). It has almost twice the power reserve of the non certified ETA powered Pelagos at 70hours, you could remove it on Friday and it shouldn’t miss a beat come Monday morning.
Hopefully this trend of Tudor developing its own complete identity and brand will continue. Tudor has shown it can compete with the best of them and at this pace will only continue to do so. I can only hope the MT56xx calibre will expand to other models in the Tudor line. (a 5-line black bay, nudge, nudge)
SPECS FOR GEEKS
Manufacturer & Calibre:
Tudor; MT5612, MT5621 (with power reserve indicator)
26 jewels (MT5612)
28 jewels (MT5621)
Screw type regulator with silicone balance spring
28.8k bph, 4Hz
Hour, minutes, and seconds with hack function
Instant snap date with rapid manual change setting
Power reserve indicator (MT5621)