The Seiko/TMI/SII caliber NH35A is a hand-windable, hacking upgrade from the Seiko caliber NH25. It is one of the world’s most popular automatic movements and is widely available in many affordable/microbrand watches. Time Module aka Seiko Instruments labels the NH calibers as part of the “Basic” Mechanical Series. They also have NE calibers that are labeled as “Premium” Mechanical Series.
NH35A Also Known As…
It’s also important to note that the Seiko NH35A movement is basically an unbranded version of the Seiko caliber 4R35. for example, the NH36 is an unbranded version of the 4R36 (day + date) found in the Next Generation Orange Monster. More information here.
In the technical documentation, Time Module claims that the NH35A accuracy range is within -20~+40 seconds per day under normal conditions. They recorded these accuracy measurements without the date complication being active. This shouldn’t have any noticeable bearing on the accuracy, but it’s interesting nonetheless.
Note: When you attempt to get a measurement of your watch’s accuracy, it’s important to make sure your watch is fully wound or the lack of power reserve may skew the test results. TMI states that measurements should be done within 10-60 minutes after the movement is fully wound up.
Winding the Mainspring
So what does fully wound up mean? The NH35A should be fully wound after about 55 manual turns of the crown.
This movement is also equipped with the Seiko Magic Lever, so shaking the watch side to side should get it going almost immediately.
Crown Position Functions:
0 (against the case): Clockwise = Manual Winding / Counterclockwise = Nothing
1 (pulled out one click): Clockwise = nothing / Counterclockwise = Date setting
2 (pulled out two clicks): Time setting clockwise and counterclockwise
While many watch brands that use the NH35A will opt for a custom rotor (oscillating weight), as of the official tech sheets from March 2017, two stock rotors are available depending on the country of origin: Japan or Malaysia.
At the time of this post, replacement prices for the caliber NH35A were found online for around $46.00 USD. Buy it here