September 26, 2026

What Is the TMI Seiko NH34 GMT Movement?

By Brian Costello, Co-Founder of Seaborne Trading Company

If you've spent any time looking at automatic GMT watches — particularly watches from independent and microbrand companies — you've probably run across the letters and numbers:

NH34.

The TMI Seiko NH34 is an automatic mechanical GMT movement with four central hands, a date display and the ability to track a second time zone.

It is also the movement inside the Seaborne WaveCatcher GMT.

But what exactly is an NH34? Who makes it? Why is it sometimes called a “Seiko NH34”? Is it a Caller GMT or a Flyer GMT? And most importantly:

Is it actually a good movement?

Let's get into it.

TMI NH34 at a Glance

Manufacturer: TMI / Time Module
Corporate family: Seiko Group
Movement type: Automatic mechanical GMT
GMT type: Caller GMT
Jewels: 24
Frequency: 21,600 vibrations per hour / 3 Hz
Power reserve: More than 41 hours when fully wound
Functions: Hours, minutes, seconds, date and independently adjustable 24-hour GMT hand
Hand winding: Yes
Hacking seconds: Yes
Movement height: 5.32mm
Manufacturer-rated static accuracy: -20 to +40 seconds per day
Used by Seaborne in: The WaveCatcher GMT

Who Makes the NH34?

The NH34 is manufactured by TMI — Time Module, a movement supplier within the Seiko Group.

That's where some naming confusion begins.

You'll routinely see the movement described online as:

TMI NH34

Seiko NH34

Seiko/TMI NH34

All three are generally referring to the same caliber people are talking about.

For our purposes, TMI NH34 is the most precise name because TMI is how the manufacturer identifies and sells the movement.

But calling it the “Seiko NH34” is understandable because of TMI's relationship with the Seiko Group — and it's also how a lot of watch buyers search for it.

TMI launched the NH34 GMT movement in 2022, adding a center 24-hour GMT hand to its NH mechanical movement family.

What Does the NH34 Actually Do?

The NH34 is a traditional automatic mechanical movement with one important addition:

A fourth central hand that rotates once every 24 hours.

Your regular hour and minute hands tell you local time.

The additional GMT hand points to a 24-hour scale and can be set to another time zone.

So you might have:

Regular hands: Boston — 10:00 AM

GMT hand: Fiji — 2:00 AM

One watch.

Two places.

If you want a deeper explanation of how GMT watches work in general, we've covered that separately in our guide, What Is a GMT Watch? A Simple Guide to Tracking Two Time Zones.

Here, we're interested specifically in the machinery doing the work.

Is the NH34 Automatic?

Yes.

The NH34 is a mechanical automatic movement.

As you wear the watch, a weighted rotor inside the movement turns with the movement of your wrist and winds the mainspring.

That mainspring stores the energy used to operate the watch.

No battery.

If the watch has stopped, you can also wind the NH34 manually using the crown.

Once sufficiently wound, normal wrist movement helps keep it running.

That's one reason the NH34 made sense for the WaveCatcher.

We wanted the WaveCatcher to feel like a mechanical watch first and a GMT complication second.

The movement is part of the experience.

How Long Is the NH34 Power Reserve?

TMI rates the NH34 at more than 41 hours of power reserve when fully wound.

In practical terms, that means an NH34 can usually continue running for well over a day after you take it off.

Leave it unworn long enough, however, and eventually it will stop.

That's normal.

It's an automatic mechanical watch.

If you've left your WaveCatcher on the dresser for several days, you'll likely need to wind it and reset the time before putting it back on.

Some people consider that an inconvenience.

Mechanical-watch people tend to consider it Tuesday.

Does the NH34 Hack?

Yes.

The NH34 has what is commonly called hacking seconds or a stop-second function.

When you pull the crown into the time-setting position, the seconds hand stops.

That allows you to set the watch more precisely against a reference time before pushing the crown back in and restarting the movement.

Is this absolutely necessary to survive modern life?

No.

Is it the sort of feature watch enthusiasts appreciate?

Definitely.

Can You Hand-Wind the NH34?

Yes.

In addition to automatic winding from the rotor, the NH34 can be manually wound through the crown.

That's useful if the watch has completely stopped.

Rather than shaking your wrist around like you're trying to get someone's attention across a crowded restaurant, you can simply give the crown a series of turns to put energy back into the mainspring.

Much more dignified.

Is the NH34 a Caller GMT or a Flyer GMT?

The NH34 is a Caller GMT, sometimes called an Office GMT.

That means the 24-hour GMT hand can be adjusted independently.

The regular local hour hand does not independently jump forward or backward in one-hour increments the way it does on a Flyer or Traveler GMT.

There is an entire corner of the internet devoted to explaining why that makes a Flyer GMT “better.”

We don't really agree with that as a blanket statement.

They're designed for different kinds of use.

A Flyer GMT Makes Sense When You Move

Imagine you fly from Boston to Los Angeles.

On a Flyer GMT, you can jump the regular hour hand back three hours to California time while leaving the GMT hand showing Boston time.

That's extremely convenient for someone who frequently travels between time zones.

A Caller GMT Makes Sense When the Other Place Moves

With the NH34, your regular hands stay on local time and you independently move the GMT hand to whichever other place you want to track.

And for the way we designed the WaveCatcher, we think that's a very natural fit.

The idea behind the watch isn't necessarily:

“I just landed in another time zone.”

It's often:

“I'm here. What time is it there?”

"There" might be Pipeline.

Cloudbreak.

Rincon.

Or somewhere else you'd rather be.

That's why we've never considered the Caller architecture a compromise on the WaveCatcher.

For this particular watch, we actually like it.

Is a Flyer GMT Better Than the NH34?

If you cross international time zones constantly, a Flyer GMT may absolutely be more convenient for you.

That doesn't make it inherently a better movement.

It makes it better suited to that particular job.

Think about it another way.

A pickup truck is better than a sports car at towing a boat.

That doesn't settle the question of which is the better automobile.

It tells you which one is better at towing a boat.

Same idea.

If your GMT use case is repeatedly changing your local time while preserving home time, the Flyer architecture is excellent.

If your local time generally stays put and you want to change which distant location you're following, a Caller GMT is extremely intuitive.

Choose the tool for the job.

How Accurate Is the NH34?

TMI specifies the NH34 with a static accuracy range of -20 to +40 seconds per day under its stated testing conditions.

That is a manufacturer's specification — not a promise that every movement will gain or lose exactly that amount every day.

Mechanical watch accuracy is affected by factors including position, temperature, how fully wound the mainspring is, and how the watch is worn.

It's also important to put the numbers into perspective.

The NH34 is a mechanical movement.

If you need a watch that deviates only a handful of seconds over an entire month, buy quartz.

Seriously.

Quartz is incredible at that.

The appeal of the NH34 isn't that it outperforms electronic timekeeping.

It's that gears, springs and a balance assembly are mechanically keeping track of two time zones on your wrist.

That's a different kind of appeal.

Why Does the NH34 Run at 21,600 Vibrations Per Hour?

The NH34 operates at 21,600 vibrations per hour, or 3 Hz.

That means its regulating system is oscillating six beats per second.

One visible result is the familiar mechanical motion of the seconds hand.

Rather than moving once per second like most quartz watches, the seconds hand advances in several smaller steps each second, creating the smoother appearance people associate with an automatic watch.

Higher-beat mechanical movements exist.

So do lower-beat movements.

Again, specifications aren't a video game where the largest number automatically wins.

The NH34's frequency is part of a mechanical package designed around practical automatic timekeeping and GMT functionality.

How Many Jewels Does the NH34 Have?

The NH34 uses 24 jewels.

No, that does not mean someone hid 24 tiny diamonds inside your watch.

Movement jewels are extremely hard synthetic bearings used at important friction points within a mechanical movement.

They help reduce wear as components rotate and interact.

The jewel count is one of those specifications watch companies love printing on things.

It's useful information.

It is not, by itself, a measurement of how good a movement is.

More jewels does not automatically mean better watch.

How Big Is the NH34 Movement?

TMI lists the NH34 at 5.32mm in height.

That's only the movement.

The finished watch has to accommodate the movement, dial, hands, crystal, caseback, water-resistance structure and — in the NH34's case — the additional central GMT hand.

That fourth hand creates a taller hand stack than a basic three-hand movement.

These things matter when you're designing an actual watch rather than simply comparing specifications on a screen.

The WaveCatcher ultimately measures 13.7mm thick, including its sapphire crystal and exhibition caseback.

NH34 vs. NH35: What's the Difference?

The NH34 and NH35 belong to the same broader TMI NH mechanical movement family.

But they serve different purposes.

The NH35 is essentially a three-hand automatic movement with a date.

The NH34 adds a center 24-hour GMT hand and second-time-zone functionality.

Both are listed by TMI at 5.32mm in movement height and both operate at 21,600 vibrations per hour.

But the additional GMT hand is the important difference.

If you don't need another time zone, the NH35 is a straightforward automatic movement.

If you want a true second time-zone display, that's where the NH34 comes in.

Is the NH34 the Same as Seiko's 4R34?

This is another common question.

Seiko uses a movement called the 4R34 in its own GMT watches.

The TMI NH34 and Seiko 4R34 share very similar headline specifications, including:

24 jewels

21,600 vibrations per hour

Automatic and manual winding

Approximately 41 hours of power reserve

A center 24-hour GMT hand

Date display

Hacking seconds

That's why you'll frequently see the two movements discussed together.

The important distinction for a Seaborne owner is straightforward:

The movement used in the WaveCatcher is the TMI NH34.

That's the designation we use.

Is the NH34 a Good Movement?

We think so.

Obviously, we chose one.

But “good” needs a little context.

If you're comparing the NH34 to an extremely expensive Swiss GMT movement with a Flyer GMT architecture, chronometer-level regulation and significantly more elaborate finishing, you're comparing movements designed for very different watches and price points.

That's not particularly useful.

For the WaveCatcher, we wanted:

An automatic mechanical movement

Real second-time-zone functionality

An independently adjustable GMT hand

Hand winding

Hacking seconds

A useful power reserve

A movement from an established movement manufacturer

And we wanted to build the finished watch at a price that didn't turn a colorful surf-inspired GMT into a financial planning decision.

The NH34 checked those boxes.

Why We Chose the NH34 for the WaveCatcher GMT

Movement selection isn't supposed to happen in isolation.

You start with the watch you're trying to make.

The WaveCatcher was designed around travel, surf destinations and the idea of keeping another place somewhere on your wrist.

We wanted it mechanical.

We wanted it automatic.

We wanted an actual independently adjustable second-time-zone hand.

And we wanted the movement visible through the exhibition caseback.

The NH34 gave us that package.

But there was another reason.

The Caller GMT functionality fits the personality of the watch.

You're sitting in New England.

Your normal hands show local time.

You set the GMT hand to Hawaii.

Or Fiji.

Or somewhere else you're thinking about.

That's what the WaveCatcher was built around.

Not maximizing specifications.

Keeping another place a little closer.

The NH34 and the Seaborne Idea

We're watch people.

We like mechanical movements.

We like sapphire casebacks.

We like knowing there's a tiny machine working away underneath the dial.

But we're also not particularly interested in pretending every specification needs to become a hierarchy.

Caller versus Flyer.

Three hertz versus four.

Forty-one hours versus seventy.

At some point, you need to stop reading the specification sheet and put the watch on.

The NH34 does what we wanted the WaveCatcher to do.

It mechanically keeps local time.

It tracks somewhere else.

And when you flip the watch over, you can see it doing its thing.

That's enough reason for us.

Carry Your Adventure.

Frequently Asked Questions About the TMI Seiko NH34 GMT Movement

What is the NH34 movement?

The NH34 is an automatic mechanical GMT movement manufactured by TMI / Time Module. It displays hours, minutes, seconds, date and a second time zone through an additional center 24-hour GMT hand.

Is the NH34 made by Seiko?

The NH34 is produced and sold by TMI / Time Module, which is associated with the Seiko Group. This is why the movement is commonly described as the “Seiko NH34,” although TMI officially identifies the caliber as NH34.

Is the NH34 automatic?

Yes. The NH34 is an automatic mechanical movement that winds through wrist movement and can also be manually wound through the crown.

Is the NH34 a Caller GMT?

Yes. The NH34 is a Caller or Office GMT. Its 24-hour GMT hand can be independently adjusted while the regular local hour hand remains tied to the main time setting.

Is a Caller GMT worse than a Flyer GMT?

No. The two designs prioritize different uses. Flyer GMTs are especially convenient for frequently changing local time while traveling. Caller GMTs make it easy to leave local time alone and change the second time zone being tracked.

What is the NH34 power reserve?

TMI specifies the NH34 at more than 41 hours when fully wound.

How accurate is the NH34?

TMI lists a static accuracy specification of -20 to +40 seconds per day under its specified testing conditions. Actual mechanical-watch accuracy can vary based on use, position, temperature and state of wind.

How many jewels are in an NH34?

The NH34 has 24 jewels.

Does the NH34 have hacking seconds?

Yes. The stop-second function allows the seconds hand to stop while setting the time.

Can you manually wind an NH34?

Yes. The NH34 supports both automatic and manual winding.

What is the difference between the NH34 and NH35?

The NH35 is a three-hand automatic movement with a date. The NH34 adds a central 24-hour GMT hand and independently adjustable second-time-zone functionality.

What watch does Seaborne use the NH34 in?

The Seaborne Surfer WaveCatcher GMT Automatic uses the TMI NH34 movement. We chose it for its automatic mechanical operation, GMT functionality and Caller GMT architecture, which fits the WaveCatcher's concept of tracking a faraway destination while keeping local time on the main hands.

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