| Manufacturer | Seiko Instruments Inc. aka SII / Hattori / TMI |
| Caliber Number | VK64, VK64A |
| Type | Quartz (mecaquartz) |
| Lignes | 13.5”’ |
| Diameter | 30.80mm x 29.10mm |
| Casing Diameter | 29.00mm |
| Height | 5.10mm |
| Battery Cell Number | 394 (SR936SW) |
| Battery Life | ~3 years |
| Jewels | 0 |
| Frequency | 32,768Hz |
| Quartz Type | Tuning fork type quartz crystal |
| Stem | 351177 (tap 10) or 351892 (tap 11) |
| 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 |
| Hacking Seconds? | Yes |
| Country of Manufacture | Japan (assembled) |
| Known Models | AVI-8 Flyboy, EMG Horizon Chrono, Autodromo Ford GT, Brew Method, Brew Retrograph (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 chronograph movement that uses quartz technology for the main functions of the watch, and a mechanical module for operating the chronograph. Learn more here.
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.
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:
The Seiko labeled caliber number for the VK64 is 6T64. 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.
Examples of watches with caliber VK64:
The watch below is an AVI-8 Flyboy with a VK64A inside.
Additional Resources:
