Sellita · Sellita SW330-2 GMT

Christopher Ward C63 Sealander GMT, Formex Reef and Sinn 105 UTC power reserve: inside the Sellita SW330-2

The Christopher Ward C63 Sealander GMT, C65 Dune GMT, Formex Reef GMT and many microbrand GMTs run on the Sellita SW330-2. From full it lasts about 56 hours, a little over two and a quarter days; older SW330-1 watches such as the Sinn 105 St Sa UTC are rated at 42.

Updated September 2026 · Based on manufacturer specs, published reviews and watchmaker/owner reports

Watches that use the Sellita SW330-2

The SW330 is the standard Swiss GMT movement for brands outside Swatch Group. It adds a 24-hour hand to Sellita's slim SW300-1, and it's the reason a Swiss GMT can cost under a thousand dollars. Most watches on sale now have the SW330-2; some earlier and still-current models use the SW330-1. The table covers the ones people search for most.

Specs at a glance

History and where it came from

Sellita introduced the SW330-1 in 2015 as its answer to the ETA 2893-2, the GMT version of the 2892. With ETA supplies to outside brands shrinking, it quickly became the default for independent GMTs, including the Sinn 105 UTC, early Monta Atlas watches and Christopher Ward's first Trident GMTs.

In 2020 Sellita updated it to the SW330-2, changing six components to improve how the GMT hand works and sets. Owners of SW330-1 watches had reported GMT hands that drifted slightly out of line with the hour markers. Beans & Bezels notes that Christopher Ward says the problem was fixed in the new version. In 2021 the whole SW300 family got a new barrel and mainspring, raising the reserve from 42 to 56 hours. That's why a current C63 Sealander GMT or Formex Reef runs noticeably longer than a Sinn 105 UTC.

Accuracy in the real world

Accuracy depends on grade and on how much the brand regulates it. Formex uses COSC-certified movements and then tests them again after casing. Christopher Ward doesn't publish a grade for the C63, but Beans & Bezels measured its review watch at about +9 s/day dial up and +7 crown up on a timegrapher, well inside a standard Sellita tolerance. Unimatic lists ±5 s/day for its SW330-2 watches.

As a 4 Hz movement with a normal regulator, it's easy for a watchmaker to adjust. The GMT hand has no effect on timekeeping.

Reliability and servicing

The SW330 shares its base with the SW300-1, which has a clean record, and parts are widely available. Service intervals of four to five years are typical, and any watchmaker who handles the SW300 or ETA 2893 can service it.

The known weak point was the SW330-1's GMT hand drifting between hourly positions, which the SW330-2 addresses. If you're buying a used SW330-1 watch, check that the GMT hand lines up with the hour markers when it clicks forward.

Quirks worth knowing

• It's a caller, not a flyer. The 24-hour hand jumps in one-hour steps while the local hour hand stays put. That's ideal for tracking a second zone from home, like calling the office overseas. When you travel, you move the main hands and then reset the GMT hand, which takes under a minute. Rolex- and Tudor-style "flyer" GMTs work the other way round.
• One crown position, two jobs. Pull the crown to the middle position: turn one way to move the GMT hand, the other to change the date.
• Date danger zone. Avoid quick-setting the date late in the evening. Here's why.
• 42 or 56? An SW330-1, or an SW330-2 made before 2021, has the 42-hour barrel. The brand's spec sheet for the year you bought it is the best guide.

How it compares

• ETA 2893-2: the original caller GMT, now mostly limited to Swatch Group brands. Same size and function, about 42 hours.
• Sellita SW300-1: the same base without the GMT hand, and the same 56-hour barrel.
• Seiko 6R54: Seiko's caller GMT with a 72-hour reserve at 3 Hz, in the Presage and Prospex GMTs.
• Seiko NH34: the cheap caller GMT in Seiko 5 Sports GMTs and many microbrands; 41 hours and a looser tolerance.
• Rolex 3285 and Tudor MT5652: flyer GMTs with 70-hour reserves, at several times the price.

Living with the 56-hour reserve

Fifty-six hours is just short of a full weekend. Take your Christopher Ward C63 Sealander GMT off at 6pm on Friday and, from a full wind, it keeps going until about 2am on Monday, so it stops a few hours before you pick it up. If you keep it on through Friday evening and put it on a little earlier on Monday morning, it probably makes it. A Sinn 105 UTC with the older 42-hour SW330-1 stops around noon on Saturday.

A stopped GMT is more work to restart than a simple three-hander, because you set the time, the second time zone and the date. That's a good reason to keep it going. Watch Winder counts down the reserve for each watch you own and reminds you before it stops, so you can put the GMT on for an evening instead of resetting three things on Monday. To check a particular weekend, try the "Will my watch stop?" calculator.

Verdict

The SW330-2 is a solid, easy-to-service GMT that made the Christopher Ward C63 Sealander GMT and Formex Reef possible at their prices. With the newer barrel it runs well over two days. The limits are the caller layout, which suits office-to-overseas use better than frequent flying, and the reserve, which falls just short of a full weekend. If you travel constantly, a flyer GMT will suit you better. If you track a second zone from home, it's hard to beat.

FAQ

How long does the Christopher Ward C63 Sealander GMT run off the wrist?

Its Sellita SW330-2 runs about 56 hours from a full wind, a little over two and a quarter days. Less if it was only partly wound when you took it off.

Is the Christopher Ward C63 Sealander GMT a true GMT?

It's a caller GMT: the 24-hour hand is set independently in one-hour jumps, while the local hour hand isn't. It tracks two time zones well but is slower to change local time when you travel.

What is the power reserve of the Formex Reef GMT?

Formex quotes 56 hours for the COSC-certified Sellita SW330-2 in the Reef GMT.

How long does the Sinn 105 St Sa UTC run?

Sinn's 105 St Sa UTC uses the Sellita SW330-1, which is rated at about 42 hours from a full wind.

Does the SW330-2 hack?

Yes. The seconds hand stops when you pull the crown fully out to set the time, and the movement can be wound by hand.

What's the difference between the SW330-1 and SW330-2?

The SW330-2, from 2020, has six revised parts that improve the GMT hand's setting and alignment. Movements made since 2021 also have the 56-hour barrel rather than the earlier 42-hour one.

How do I set the GMT hand on a Christopher Ward C65 Dune GMT?

Pull the crown to the middle position and turn it one way to jump the GMT hand in one-hour steps; turn it the other way to change the date. Pull it fully out to set the local time.

Sources

• Unimatic: Sellita SW330-2 specifications and instructions
• Grail Watch Reference: SW330-1 and SW330-2
• Beans & Bezels: Christopher Ward C63 Sealander GMT review
• Formex: Reef GMT Automatic COSC 300M
• Monochrome: Sinn 105 St Sa UTC collection

Keeping it running

• On an average day an automatic gains roughly 4 hours of reserve per hour on the wrist, so about 14 hours of wear fills the Sellita SW330-2 GMT. Desk days charge more slowly.
• Most automatics can also be wound by the crown. If yours has stopped, a few dozen turns gets it going before you put it on.
• Off the wrist it stops about 56 hours after it was last full. Stopped sooner?
• On a watch winder, start at about 650 turns per day, both directions. Winder settings for every movement.
• If it does stop, don't set the date between 9pm and 3am. Check if it's safe.

All Sellita movements

Never let it stop

Watch Winder counts down the reserve of every watch you own and reminds you before one stops. It already knows the Sellita SW330-2 GMT: type your watch's name and the reserve fills itself in.

Manufacturer's published figure. Real reserve varies with the watch's age and service; check your manual.