Before You Diagnose Anything: Which Tudor Movement Do You Actually Have?

Almost every bad piece of Tudor advice on the internet comes from the same mistake: someone applies a fact about one movement to a watch that has a completely different one inside it.

A Black Bay from 2014 and a Black Bay from 2024 look nearly identical on the wrist. Mechanically they have almost nothing in common. One has a roughly 40-hour power reserve, a steel hairspring, and parts you can buy on the open internet for pocket change. The other has 70 hours, a silicon hairspring, and parts Tudor will not sell to your local watchmaker at any price.

So before any of the diagnostic posts in this series will help you, you need to know which of three eras your watch belongs to.

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The three eras

Vintage (roughly 1955–1990) — Fleurier-based and early ETA movements. Submariners, Oyster Princes, Rangers, the Monte Carlo and Home Plate chronographs, the Big Block.

Modern ETA (roughly 1990–2016) — Tudor bought Top Grade ETA movements and modified them. Prince Date, Submariner 79090, the first-generation Black Bay and Pelagos, Heritage Chrono, Fastrider.

Manufacture / MT (2015–present) — in-house calibres made by Kenissi. Every current Black Bay, Pelagos, Ranger and Black Bay Chrono.

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Vintage era

Calibre	Base	Found in
Tudor 390	Fleurier / FEF	Submariner 7922, 7924, 7928; Oyster Prince
Tudor 2461	ETA 2451	Early Oyster Prince
ETA 2483	ETA 2452	Submariner 7016; Ranger 7965, 7995
ETA 2484 (date, no quickset)	ETA 2452	Submariner 7021; Prince Oysterdate 7966, 7996, 9050
ETA 2776 (hacking, no date)	ETA 277x	Submariner 9401/0, 94010; Ranger 90200/90220
ETA 2783 / 2784 (hacking, date)	ETA 277x	Submariner 9411/0, 94110; Oysterdate 9050/90800
Valjoux 7734	Venus 188 lineage	Chronograph 7031/0, 7032/0 "Home Plate"
Valjoux 234	Valjoux 23/72 family	"Monte Carlo" 7149/0, 7159/0, 7169/0
Valjoux 7750	—	"Big Block" 9430/0, 94200/94300/94400

Two corrections worth making now, because both circulate widely:

The Tudor 390 is not an in-house movement. The Ranfft movement database indexes it literally as "Tudor 390 (FEF 380)," and Tudor's own technical catalogue is titled "caliber 390 (FEF 350, 380)." It is a Fleurier base with a Tudor-designed automatic module bolted on — and as a later post in this series covers, that module is the single most problematic thing in vintage Tudor.

And there is no evidence Tudor ever used the Valjoux 7736, despite it turning up in reference lists. Tudor's chronographs went 7734 → 234 → 7750.

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Modern ETA era

Tudor calibre	ETA base	Found in
T601 / "Calibre 2824"	ETA 2824-2	Submariner 79090/79190, Prince Date, Hydronaut, Black Bay 79220 (2012–16), Black Bay 36 (79500), Pelagos 25500TN (2012–15)
T603	ETA 2834-2	Prince Date-Day 76200/76213/76214
T201	ETA 2671	Clair de Rose, Glamour Date, Style 28
T401	ETA 2892-A2 + Dubois Dépraz module	Heritage Chrono 70330, Grantour Chrono Fly-Back
T401-901	ETA 2892-A2 + alarm module	Heritage Advisor 79620
(unnumbered)	Valjoux 7750	Prince Date chronographs 79260/79270/79280, including the "Tiger" Woods editions
(unnumbered)	ETA 7753	Sport Chrono, Grantour Chrono, Fastrider / Black Shield 42000

The Heritage Chrono 70330 is not a 7753. This one matters, because it completely changes the service story. It is an ETA 2892-A2 with a Dubois Dépraz chronograph module on top. The 55-jewel count gives it away — that's a 21-jewel base plus a module. The layout (running seconds at 3, a 45-minute counter at 9, date at 6) is a module configuration, not an integrated chronograph.

What Tudor actually changed

Tudor didn't just drop stock ETAs into cases. The widely-reported picture is that it bought Top Grade ébauches — Glucydur balance, Anachron hairspring, five-position adjustment — then made its own modifications:

• KIF shock protection replacing Incabloc (what Rolex has always used)
• A Triovis regulator replacing ETA's ETAchron, at least on later examples
• A Tudor-signed and decorated rotor
• Regulated to chronometer standards — but without paying for COSC certification

A caveat on that list: Tudor has never published it. It comes from watchmakers and dealers on the forums, plus movement sellers offering "Tudor Calibre 2824 — Top Grade ETA modified with KIF shock absorbers and Triovis regulation" as physically distinct parts. It's well-attested but not manufacturer-confirmed, and the Triovis change specifically is described as arriving "towards the end of the Prince Submariner run," so it won't be on every watch.

One nice side effect of Tudor's work: the date change on these is semi-instantaneous — it starts around 23:55 and snaps at midnight. A stock 2824 crawls. So if your Tudor's date takes an hour to change, that's abnormal for a Tudor, even though it would be normal for the base movement.

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Manufacture era (in-house MT)

Calibre	Power reserve	Certification	Introduced	Found in
MT5621	70 h	COSC	2015	North Flag
MT5612	70 h	COSC	2015	Pelagos
MT5601	70 h	COSC	2016	Black Bay (no date)
MT5602	70 h	COSC	2016	Black Bay
MT5602-U	70 h	COSC + METAS	2023	Black Bay Ceramic
MT5652	70 h	COSC	2018	Black Bay GMT
MT5652-U	65 h	COSC + METAS	2022	Pelagos FXD GMT
MT5402	70 h	COSC	2018	BB58, Ranger 39
MT5400	70 h	COSC	2023	BB54, Pelagos 39
MT5400-U	65 h	COSC + METAS	2026	New BB58
MT5450-U	65 h	COSC + METAS	2024	BB58 GMT
MT5813	70 h	COSC	2017	Black Bay Chrono — Breitling B01 base

Note the power reserve column carefully, and note that the "-U" suffix does not tell you the number. MT5400-U, MT5450-U, MT5652-U and MT5662-2U are 65 hours. But the MT5602-U in the Black Bay Ceramic is METAS-certified and still 70. If you own a 2024-or-later BB58 GMT, or the 2026 BB58, and you're measuring your reserve against a 70-hour figure, you're measuring against the wrong number. METAS independently verifies the claimed reserve as part of certification, so 65 is the real, tested figure for those calibres.

Who actually makes these

Kenissi, founded by Tudor (part of the Rolex Group) in 2016, with its Le Locle manufacture fully operational by 2022. Chanel holds a 20% minority stake. Kenissi also supplies Breitling, TAG Heuer, Norqain, Fortis, Bell & Ross and Jacob & Co.

That last fact is more useful than it sounds. Because Kenissi shares components across all those brands' calibres, some MT parts are theoretically obtainable outside Tudor's own supply chain — which is the main loophole independent watchmakers have, given that Tudor doesn't sell parts to them.

Every MT calibre Tudor documents shares the same architecture: a tungsten monobloc rotor on ball bearings, a traversing balance bridge, a free-sprung variable-inertia balance, and a silicon balance spring.

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Four things "everyone knows" about MT calibres that are wrong

Worth clearing up before you diagnose anything.

1. "They only wind in one direction." No. Every MT calibre is bidirectional — Tudor's MT5612 movement page says "its self-winding system is bidirectional," and the current BB58 product page specifies a "bidirectional rotor system." The confusion comes from manual winding, which is clockwise-only. That's true of almost every watch ever made.

2. "Tudor's accuracy spec is looser than COSC." It's the opposite. COSC certifies the bare movement at −4/+6 seconds a day. Tudor's spec is −2/+4 seconds a day tested on the fully assembled watch — a tighter standard applied at a harder stage. METAS "-U" calibres are 0/+5.

3. "MT calibres have a slow, crawling date change." No — the date models are instantaneous by design. Which means a crawling or half-stuck date on an MT5612 or MT5652 isn't a quirk. It's a symptom, and on one specific model it's a known defect.

4. "The silicon hairspring makes it antimagnetic." As of 2026, only the METAS -U calibres are certified to 15,000 gauss. On every other MT calibre, the escape wheel, pallet fork, balance staff, pivots and gear train are all still steel — and steel magnetizes. Silicon removes the main magnetism failure mode, not all of them. (Tudor has said that "eventually, all new TUDOR watches will be" Master Chronometer certified, so this distinction has a shelf life — check what your specific calibre carries.)

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How to find your calibre

The reference number is on the caseback or, on modern watches, engraved on the rehaut (the inner ring under the crystal) and printed on the guarantee card. Match it against the tables above. If you're buying pre-owned and the seller can't tell you the reference, that's information too.

Once you know the calibre, the rest of this series will make sense — and you'll be able to skip the two-thirds of it that don't apply to you.

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Sources: Tudor — Manufacture Calibre · Tudor — Movement 5612 · WatchBase — Tudor calibers · Caliber Corner — Tudor T601 · Grail-Watch — Survey of Kenissi movements · Monochrome — Inside Tudor and Kenissi · Rolex Forums — Tudor ETA modifications