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Sii Caliber Vh31 Drawing

SII Caliber VH31

Sii Caliber Vh31 Drawing

ManufacturerSeiko Instruments Inc. / SII / Hattori / TMI
Caliber NumberVH31, VH31A
TypeQuartz (mechaquartz)
Lignes
10.5”’
Diameter
23.70mm
Casing Diameter
23.3mm
Height3.45mm thick
Battery Cell Number371 (SR920SW)
Battery Life
~2 years
Jewels
2
Frequency32,768 Hz
Quartz TypeTuning fork type quartz crystal
Stem351177/tap 10 or 351892/tap 11
Hand Sizes1.20mm / .70mm / .17mm
Hacking?
Yes
FunctionsCentral hours, central minutes, central seconds
Country of ManufactureJapan
Known Models (Too many to list. Add your watch in the comments below…)

The Seiko Instruments (SII) caliber VH31 is part of the VH family of hybrid mechanical quartz (mechaquartz) movements that Seiko refers to as their Sweep Second Quartz Series. It is a true no-date 3-hander with 2 jewels, made in Japan. Official technical documentation for the VH31A was found dated as far back as August 2016.

VH31 VS VH31A:

What is the difference between VH31 and VH31A? Nothing. VH31 is the base caliber designation and the trailing letter is an evolution or upgrade indicator, A being the first version produced. At the time of this post, there is not a VH31B and may never be one if Seiko does not feel the need to change anything.

Sweeping Seconds:

As a mecaquartz type of movement, the second hand on the VH31 has a rather smooth sweeping motion, unlike most quartz watches that impulse with a ticking motion. The seconds on a VH31 sweep at 4 beats per second which is slower than a typical automatic (for example the NH35A beats 6 times per second), but much smoother than a regular 1 beat per second quartz.

How TMI describes it:

“Centre second hand moves 4 times per second, resembles mechanical movements.”

Accuracy Rating:

Seiko/Time Module states that the expected accuracy of this calibre is +/- 15 seconds per month at normal operating temperatures of -5C to + 50C (23F – 122F). There is no way to regulate or adjust this movement.

Battery Replacement:

The VH31 battery life is about 2 years. The cell number for replacement is 371 (SR920SW).


To change the battery, use your tool to gently hold the retaining tab to the side, allowing the battery to pop up.

Sii Caliber Vh31 Battery Replacement

VH31 Replacement Prices:

At the time of this post, replacement prices for this movement were found online in the range of $7.95 to $14.95.

TMI/SII/Hattori:

You might find this caliber VH31 listed as being produced by SII aka TMI (Time Module Inc) aka Seiko Instruments Inc. Some are signed SII and others are signed TMI. Learn more about the different names here.

Video:

Here is a short dial side video to show the smooth sweeping seconds on the VH31. At a quick glance you’d think it was an auto with a stuttering seconds hand!

Additional Resources:

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