The Seiko/TMI/SII caliber NH35A is a hand-windable, hacking upgrade from the Seiko caliber NH25A(read: NH25A vs NH35A). The earliest documentation on this movement that we were able to find was issued on 2/14/2011, this also corresponds with the 2011-2012 time frame that the first NH35A powered watches started hitting the market.
The NH35A is currently 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. Read: NHXX caliber differences.
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
The NH35A has several variations depending on a few variables. While all are considered to be “NH35A”, there can be different reference numbers based on each combination of variable options. This information is mostly useful for watch manufacturers, but can also be useful if you intend on swapping your movement for any reason. The variations include the location where the movement was produced, date position, calendar color, and hand fitting type.
From the factory, the NH35A has the date at 3:00 or 6:00. The 3:00 date version is the most common.
To determine which date position your raw movement has, point the crown to the right and look for the number that reads from left to right – is it at 3:00 or 6:00? The location will determine the way the dates are printed on the datewheel. If your watch has a date in a different location, say a tilted date at 4:00, then it means the watch manufacturer used an NH35A with a 3:00 date position and cutout the date window at the 4:00 position.
Also keep in mind that although unlikely, it is possible the watch manufacturer printed a custom datewheel – again, possible but unlikely.
Date Disc Color
The NH35A datewheel (aka date disc) is available from the factory in two versions: white background with black text, or black background with white text. The white datewheels with black text are the most common.
Part of the reference number also determines the origin of production (see the rotor section below). J is for Japan, M is for Malaysia.
Hand Fitting Type
NH35A movements can be made for Hand Type M or L. Type L is like a high hand version. This affects the overall height of the movement from the bottom to the top of second hand pinion. The thickness of the NH35A is 5.32mm, but the overall height including the hands can be about 7.6mm (M) or 8mm (L).
When designing a watch from scratch, this is useful for determining the thickness of your case, dial, space between dial and crystal, etc. When modding your current watch or swapping movements, be sure that you order the correct Hand Fitting Type or you may end up with hands sticking up too far away from the dial.
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 $38.27 USD. Buy it here