A power-reserve variant of the MT5612
The MT5621 is mechanically identical to the MT5612 base used in the standard Pelagos 25600/25610: same 4 Hz beat, 70 h reserve from a single barrel, silicon hairspring, free-sprung balance with Microstella-style variable inertia, COSC chronometer rating. The single addition is the power reserve indicator, a small subdial at 9 o'clock showing the remaining wind. Tudor uses the MT5621 only in references where the dial layout supports a PR display: the LHD destro-version Pelagos and the discontinued North Flag.
In the Pelagos LHD
The Pelagos LHD (ref. 25610TNL, launched 2016, hence the LHD = "Left-Hand Destro" designation) is the unusual mirror-image variant of the standard Pelagos: the crown sits on the left side of the case at 9 o'clock, and the dial includes the power-reserve subdial at 3 instead of the date window. The combination is unusual: a left-hand dive watch with an in-house power-reserve display is something only Tudor offers in the modern professional dive segment. The MT5621 was developed specifically for this dial architecture.
In the North Flag
The MT5621 also powered the Tudor North Flag (ref. 91210N), launched in 2015 as Tudor's first watch with an in-house manufacture caliber. The North Flag was a 40 mm angular-cased adventure watch with a black ceramic bezel insert and a contrasting yellow-and-black dial inspired by the 1952 British Greenland expedition. The North Flag was the showcase watch for the launch of the Tudor manufacture caliber programme; the Pelagos line followed shortly with the related MT5612 and MT5621. The North Flag has since been discontinued (2020), making the MT5621 unique to the Pelagos LHD in current production.
Where it sits in the Tudor caliber line
Tudor's in-house caliber family now spans:
- MT5402: 26 mm, 3-hand + date, in BB58/BB39 (compact watches)
- MT5612: 28 mm, 3-hand + date, in standard Pelagos / Black Bay 41
- MT5621: 28 mm, with power reserve, in Pelagos LHD
- MT5652: with GMT module, in Black Bay GMT
- MT5813: chronograph, in Black Bay Chrono (Breitling B01-based)
All share the same Kenissi family base architecture: 4 Hz, 70 h reserve, silicon hairspring, COSC. The MT5621 is the rarest of the family by production volume (the LHD is a niche reference) but represents the most complete spec sheet: in-house, COSC, silicon spring, free-sprung balance, 70h reserve, plus PR indicator.
Service and value
Service intervals around 5-7 years through Tudor service centres; full service runs USD 600-900. Pelagos LHD watches retail at approximately USD 5,400-5,700 new; the discontinued North Flag trades on the secondary market at USD 2,800-4,000 depending on condition and originality. For collectors, the MT5621-equipped Pelagos LHD represents a uniquely-specified Tudor: the only modern Pelagos with a power-reserve indicator, the only Tudor diver with a left-hand crown, and one of the most spec-complete watches in the Tudor catalogue.
