This article is available in French only.
The Seiko NH35 is an automatic mechanical movement made by Seiko Instruments: 24 jewels, 21,600 beats per hour, about 41 hours of power reserve, a date window, hacking seconds and manual winding. Seiko rates its accuracy at −20 to +40 seconds per day. It is the most common base for seiko mods and affordable automatic watches because it is robust, easy to service and supported by thousands of compatible parts.
NH35 specifications
| Specification | Seiko NH35 |
|---|---|
| Type | Automatic, with manual winding |
| Functions | Hours, minutes, central seconds, date |
| Jewels | 24 |
| Frequency | 21,600 beats per hour (6 beats per second) |
| Power reserve | About 41 hours |
| Accuracy (manufacturer) | −20 to +40 seconds per day |
| Hacking seconds | Yes: the seconds hand stops when the crown is pulled out |
| Diameter | 27.4 mm |
NH35, NH36, NH38, NH34: what is the difference?
- NH35: date only.
- NH36: day and date.
- NH38: no date, for a symmetrical dial.
- NH34: adds a GMT hand to read a second time zone. See how a GMT watch works.
The NH35 also exists as the 4R35, the same caliber sold inside Seiko's own watches.
How to wind and set an NH35 watch
The crown has three positions:
- Position 0 (pushed in): turn the crown clockwise to wind the mainspring by hand. 20 to 30 turns restart a stopped watch; you cannot overwind it.
- Position 1 (first click): set the date.
- Position 2 (pulled fully): set the time. The seconds hand stops so you can set it to the second.
One rule protects the date mechanism: do not set the date between about 9 p.m. and 3 a.m., when the date-change wheels are engaged. Move the hands to 6 o'clock first, set the date to yesterday, then advance the hands past midnight to today's date and on to the current time. If the crown screws down, unscrew it before setting and screw it back fully afterwards: that is what keeps the watch water resistant.
How accurate is the NH35?
Seiko specifies −20 to +40 seconds per day. A well-regulated example usually runs well inside that range, but the rate depends on position, temperature and how wound the mainspring is. Two tips:
- Test two resting positions overnight, crown up and dial up: one usually makes the watch run fast, the other slow. Use the one that cancels out its daytime drift.
- A watch that suddenly gains several minutes a day is often magnetized, by a phone, a speaker or a bag clasp. A watchmaker can demagnetize it in seconds.
Service and lifespan
Plan a service every five years or so: cleaning, lubrication and a water-resistance test. Because the NH35 is so common, any watchmaker can work on it, and the whole movement can be replaced at a modest cost if it is ever damaged. That makes NH35 watches among the easiest automatics to keep running for decades.
Watches with an NH35 movement at Modus
Most Modus watches run on the Seiko NH35: the DEPTH dive-style watches, AXIS, FIELD, PRISM, ATLAS and NAUTA. You can also build your own around it in the watch configurator. The exact caliber is listed on every product page.
Frequently asked questions
Is the NH35 a good movement?
Yes, for its price it is one of the most robust and serviceable automatic movements available. It is not a luxury-grade caliber, but it is proven and easy to repair.
How long does an NH35 run when not worn?
About 41 hours from fully wound. If you leave the watch off for more than two days, wind and reset it when you pick it up again.
Can you overwind an NH35?
No. A slipping bridle protects the mainspring once it is fully wound.
Does the NH35 hack?
Yes. Pulling the crown to the time-setting position stops the seconds hand.
