| Manufacturer | Seiko Instruments Inc. / SII / Hattori / TMI |
| Caliber Number | VK64, VK64A |
| Type | Quartz (mecaquartz) |
| Diameter | 13 1/2”’ (30.80mm x 29.10mm) |
| Casing Diameter |
29.00mm |
| Height | 5.10mm |
| Battery Cell Number | 394 (SR936SW) |
| Jewels |
0 |
| Frequency | Unknown (please comment below) |
| Quartz Type | Tuning fork type quartz crystal |
| Stem | 351177/tap 10 or 351892/tap 11 |
| Hand Sizes | 1.50/.90/.32mm |
| Functions | Hours, minutes, central chronograph seconds, 1/5 seconds, 60 minute counter at 9:00, 24 hour indicator at 3:00, date at 6:00 |
| Country of Manufacture | Japan (assembled) |
| Known Models | AVI-8 Flyboy (list yours 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.
Accuracy Rating
Seiko/Time Module states that the expected accuracy of this movement is less than +/- 20 seconds per month at normal temps. The battery life is about 3 years with normal operation.
Battery Replacement
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 switch spring with your tweezers.
Replacement Price
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.
Additional Resources: