Answer first: If your Seiko mod has a day-and-date window, it is almost certainly running a Seiko NH36. If it shows date only (or no date at all), it is an NH35. A Miyota 8-series is the alternative you will find in some slimmer dress builds. All three are genuine Japanese automatic movements - real self-winding mechanicals, not quartz - and every watch Rosevari Watches builds uses one of them.
TL;DR
- NH35 - date only, hacking + hand-winding, 24 jewels, ~41h reserve. The workhorse.
- NH36 - adds a day-of-week wheel (day + date), otherwise identical to the NH35.
- Miyota 8215/821A - Citizen-made automatic, slightly thinner, no hacking on the classic 8215, distinctive "stutter" rotor.
Why the movement is the first thing to check
The number one question we get is not about price. It is "is this fake?" So let us settle it cleanly: a Seiko mod is a watch built on genuine parts around a genuine movement, with an original or unbranded dial. That is a homage. A counterfeit is a watch with a luxury-brand logo stamped on a dial that did not come from that brand. Rosevari Watches never does the second thing. Knowing which movement is inside is how you prove to yourself the watch is the real mechanical article.
Learn the fundamentals first in What is a Seiko mod?, then come back here for the movement detail.
The Seiko NH35: the default workhorse
The NH35 (made by Seiko Instruments, the TMI division) is the most common automatic in the entire mod world for good reason. It hacks - the seconds hand stops when you pull the crown, so you can set the time to the second. It hand-winds, so you can get it running without shaking it awake. It runs at 21,600 beats per hour, carries 24 jewels, and holds roughly 41 hours of power reserve. Accuracy from the factory sits in a wide -20 to +40 seconds per day band, but in practice most settle far tighter and can be regulated closer.
If your watch shows a date only, this is your movement.
The Seiko NH36: the NH35 with a day wheel
The NH36 is mechanically the same movement with one addition: a day-of-week disc on top of the date. That is the whole difference. Same beat rate, same jewels, same reserve, same hacking and hand-winding. If you see both a day and a date window (common on Datejust-style and Explorer-style builds), you are looking at an NH36.
The Miyota 8-series: the Citizen alternative
Miyota is Citizen's movement arm, and the 8215/821A family is its long-running automatic. It is a touch thinner than the Seiko NH movements, which is why builders reach for it on slimmer dress cases. The trade-offs to know honestly: the classic 8215 does not hack, and its rotor has a noticeable directional "wobble" some owners love and some do not. It is a proven, reliable caliber that has powered millions of watches.
Full movement spec table
| Spec | Seiko NH35 | Seiko NH36 | Miyota 8215 |
|---|---|---|---|
| Type | Automatic (mechanical) | Automatic (mechanical) | Automatic (mechanical) |
| Maker | Seiko / TMI | Seiko / TMI | Miyota (Citizen) |
| Complication | Date | Day + Date | Date |
| Beat rate | 21,600 bph | 21,600 bph | 21,600 bph |
| Jewels | 24 | 24 | 21 |
| Power reserve | ~41 hours | ~41 hours | ~42 hours |
| Hacking (stop seconds) | Yes | Yes | No |
| Hand-winding | Yes | Yes | No |
| Factory accuracy | -20 / +40 s/day | -20 / +40 s/day | -20 / +40 s/day |
| Best suited to | Divers, tool watches | Day-date dress/field | Slim dress builds |
What Rosevari Watches uses - and why it matters
Every Rosevari Watches build runs a genuine Japanese automatic from this family, paired with a sapphire crystal rather than the soft mineral glass you find on cheaper mods. Sapphire resists scratches far better and is a real, verifiable spec advantage at this price. That combination - a real Seiko or Miyota automatic under scratch-resistant sapphire - is the honest heart of the value here. The five-figure look. A three-figure price.
A quick note on a movement you may see elsewhere: the VK63 is a meca-quartz chronograph movement. It is a smooth, satisfying caliber, but be clear with yourself that it is not an automatic - it runs on a battery with a mechanical chronograph module. If automatic is what you want, stick to the NH or Miyota calibers above.
Frequently asked questions
Is the NH35 a real Seiko movement? Yes. The NH35 is manufactured by Seiko Instruments (TMI), Seiko's movement division. It is the same architecture used across countless watches and is a genuine mechanical automatic.
NH35 vs NH36 - which is better? Neither is "better." They are the same movement; the NH36 simply adds a day-of-week wheel. Choose NH36 if you want day + date, NH35 if you only want a date or a cleaner dial.
Why do some mods use Miyota instead of Seiko? The Miyota 8-series is slightly thinner, which suits slim dress cases. It is a reliable Citizen-made automatic, with the trade-off that the classic 8215 does not hack or hand-wind.
Do these movements keep accurate time? Factory tolerance is wide, but most settle within a comfortable daily range and can be regulated tighter. These are mechanical watches, so expect seconds of drift per day, not the near-perfect accuracy of quartz.
What movement is in my Rosevari watch? Check the complication: date only points to an NH35, day + date to an NH36, and our slim dress pieces may use a Miyota. Every one is a genuine Japanese automatic under sapphire, backed by a 1-year AU-based warranty.
Ready to see which movement lives in each build? Browse the full range at /collections/all. Every Rosevari Watches piece ships free from Australia, is made to order in about 2 to 3 weeks (order early), and is covered by a 1-year AU-based warranty from A$289.
Written by Jordan, founder of Rosevari Watches. I build and sell these watches myself, and I would rather tell you exactly what is inside than sell you a mystery.