SII Hattori Caliber VK64A Watch Movement

Seiko Sii Caliber Vk64a Mecaquartz

Manufacturer	Seiko Instruments Inc. aka SII / Hattori / TMI
Caliber Number	VK64, VK64A
Movement Type	Quartz (mecaquartz), battery-powered, chronograph
Lignes	13.5”’
Diameter	30.80mm x 29.10mm
Casing Diameter	29.00mm
Height	5.10mm
Jewels	0
Frequency	32,768Hz
Quartz Type	Tuning fork type quartz crystal
Battery Cell Number	394 (SR936SW)
Battery Life	~3 years
Stem	351177 (tap 10) or 351892 (tap 11)
Hand Count	5
Hand Sizes	1.50mm / .90mm / .32mm
Functions	Central hours; central minutes; central chronograph seconds; 1/5 seconds; 60 minute counter at 9:00; 24 hour indicator at 3:00; date at 6:00
Chronograph Layout	3-9 (bi-compax)
Hacking Seconds?	Yes
Country of Manufacture	Japan (assembled)
Known Models	AVI-8 Flyboy, EMG Horizon Chrono, Autodromo Ford GT, Brew Method, Brew Retrograph, Yema Rallygraf, Mercer Brigadier (Add your watch in the comments below…)

The Seiko Instruments (SII) caliber VK64A is part of the hybrid mechanical quartz (mecaquartz) movement line. It is a bi-compax style chronograph movement that uses quartz technology for the main functions of the watch, and a mechanical module for operating the chronograph. Learn more here.

Seiko Sii Caliber Vk64a

Some of the topics covered in this caliber listing:

VK64 VS VK61:

There is a similar bi-compax mechaquartz caliber VK61. The main difference is that the VK64 has the chronograph subdials located at 3:00 and 9:00, with a date at 6:00. The VK61 has chrono subdials at 12:00 and 6:00, with a date at 3:00. These calibers are mechanically and technically similar enough for Seiko to combine the tech guides for each into one document.

Accuracy Rating:

Seiko/Time Module states that the expected accuracy of this movement is less than +/- 20 seconds per month at normal temps.

Sweeping Chronograph Seconds:

As a mecaquartz type of movement, the chronograph second hand on the VK64 has a rather smooth sweeping motion, unlike most quartz chronographs that impulse with a ticking motion.

Battery Replacement:

The VK64 battery life is about 3 years with normal operation – not constantly operating the chronograph for example.

After installing a fresh battery cell, remember to reset the circuit by touching the AC terminal of the circuit block (look for an arrow labeled AC pointing to a hole) and the + side of the batter or battery strap (the metal part that is holding the battery in) with your tweezers.

Replacement Prices:

At the time of this post, replacement prices for this movement were found online in the range of $17.95 to $34.95.

TMI/SII/Hattori:

You might find this caliber VK64 listed as being produced by SII aka Hattori aka TMI (Time Module Inc) aka Seiko Instruments Inc. Learn more about the different names here. Other calibers with the same base movement are VK61, VK63, VK67, VK68, VK73, and VK83.

Update: This caliber listing originally had the line “The Seiko labeled caliber number for the VK64 is 6T64.” This is incorrect as Seiko never ended up releasing a 6T64. There is a 6T63 which appears to be a tri-compax version of the VK64 – with a similar 60 minutes chronograph subdial at 9:00, 24 hour indicator at 3:00, and a date. The main differences between the layout of the 6T63 and the VK64 is that the 6T63 also has a small running seconds subdial at 6:00 and a date positioned at 4:30 (rather than 6:00 on the VK64). As of this update, Seiko does not have a 6T64, nor do they seem to have any bi-compax style watches based on the 6T caliber. In the future, if they release a 6T based model with a similar layout to the VK64, it will likely be called the 6T64 and this post will be updated accordingly.