Seiko NH34, NH35, NH36, NH38, NH70, NH71, NH72
🛠️ Basic Specifications:
- Manufacturer: SII (Seiko Instruments Inc.), Japan
- Caliber: NH35A
- Type: Automatic movement with manual winding and hacking seconds
- Movement type: Mechanical automatic
📏 Dimensions:
- Height: 5.32 mm
- Dial feet positions: At 0° and 180°
⚙️ Technical Details:
- Jewels: 24
- Beat rate: 21,600 vibrations per hour (6 beats per second / 3 Hz)
- Power reserve: Approximately 41 hours
- Winding direction: Bidirectional (Magic Lever system)
- Manual winding: Yes
- Hacking (stop seconds): Yes
⏱️ Functions:
- Display: Hour / Minute / Central seconds / Date
- Quick date setting: Yes (via crown)
- Date window position: 3 o’clock
- Hand hole diameters:
- Hour: 1.50 mm
- Minute: 0.90 mm
- Seconds: 0.20 mm
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📈 Accuracy (factory specs):
- Daily rate: −20 to +40 seconds/day
(Note: Many watchmakers regulate it to within ±10 seconds/day)
⚒️ Compatibility / Use Cases:
- Common replacements for: ETA 2824-2, Miyota 8215
- Popular for: Dive watches, field watches, pilots watches, modding projects
My experience with the movement
It is definitely the most popular movement among watchmaking amateurs. There is a very wide range of cases, dials and hands. There are countless possibilities for creating your own design. I have long since developed a building routine with the movements, but I still really enjoy creating the watches.
The movements are also available in many variants. The basic movement is the NH35B with three hands for hours, minutes and seconds as well as a date display, which does not necessarily have to be visible. In some cases, the day display can be removed from the movement before assembly. This is followed by the NH34B with GMT display (fourth hand), the NH36B with day display and the NH38B with open heart (visible balance wheels), but then without date display. Finally, there are the NH70, NH71 and NH72 models with skeletonised movements (all three versions differ in the colour of the finish). There are also versions with a separate second hand, but I have not used these due to the lack of dials and hands.
The movements are very reliable and quite accurate for their price range. However, readjustment is often necessary as there seem to be very large tolerances in the settings. This is obvious, because precise adjustments take time and time is money. The movements can be recommended without reservation for purely functional watches.