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Seiko Caliber 8T63

Seiko Caliber 8T63

Caliber Number8T63, 8T63A
TypeQuartz, Mechaquartz
Casing Diameter
Battery Cell NumberSR936SW (394)
Battery Life
~3 years
Quartz TypeTuning fork type quartz crystal
32,768 Hz (cycles per second)
Driving System
2 part step motor
Hacking Seconds?
Hand Count
FunctionsCentral hours, central minutes, small seconds at 6:00, 24 hour (military time) indicator at 3:00, 60 minute chronograph counter, date at 4:30
Country of ManufactureJapan
Known Models (Please add your watch in the comments below…)

The Seiko caliber 8T63 (actually marked 8T63A) is found in some Seiko branded watches. This mechaquartz chronograph movement is made in Japan and has zero (0) jewels. This movement has been produced by Seiko since at least 2015.

This movement is essentially the Seiko only version of the VK63. When used in Seiko watches, it may be signed with Seiko Time Corp. When found in non-Seiko watches, the VKXX will usually be signed with SII (Seiko Instruments).

8T63, 8T63A, 8T63B, etc:

8T63 is the base caliber number. The trailing letter is the version. 8T63A is the first version, therefore, 8T63 and 8T63A are the same. If there are any future updates to this caliber, the letter will change to 8T63B and so on.

Seiko 8T63 VS 8T68:

There is a similar caliber 8T68 that shares the same functionality as the 8T63. When comparing these two movements, the main difference between them is that the 8T63 shown here has the subdials at 3:00, 6:00, and 9:00. The 8T68 places the subdials at 2:00, 6:00, and 10:00. Both calibers offer a date feature between 4:00 and 5:00.

8T63 Vs 6T63:

The 8T63 is based on the older Seiko caliber 6T63. The functionality and layout on the 8T63 are similar to the 6T63, but this caliber has been updated to provide higher accuracy and better battery life.

Chronograph Functionality:

The 8T63 has a central stopwatch chronograph hand and a 60 minute totalizer at 9:00. The chronograph is only capable of counting up to 60 minutes in one second intervals. It automatically stops after reaching 60 minutes.

Operating the chronograph is similar to many chronograph watches:

  • Button A (top button) – Start
  • Button A (top button) – Stop
  • Button B (bottom button) – Reset

Resetting the Chronograph Hand to Zero:

The Seiko 8T63 is a mechaquartz movement, so the recalibration is not the same as a regular quartz chronograph since the hands are actually mechanically driven. This is one of the drawbacks of a meca-quartz movement, and if the hands are dramatically misaligned, you may need to have your watchmaker pull them off and install them again in the correct position.

After a battery change, you can try the following instructions for lining up the hands (needs confirmed):

  • When the small seconds hand on the 6:00 subdial reaches 12:00, pull the crown out to position 2 (2 clicks to time-setting mode).
  • Press the bottom pusher (button B) for 2+ seconds until the central chronograph hand turns around the dial.
  • Press the crown back in.

For chronograph troubleshooting, see the following:

Seiko Caliber 8t63 Troubleshooting

Battery Life:

In the manual, Seiko claims that a new battery installed in the caliber 8T63 should last approximately 3 years. Keep in mind that the battery will drain faster if you leave the chronograph second hand running – specifically if the chronograph is used for more than 1 hour per day.

There is also a low battery indicator which will cause the small second hand to jump every 2 seconds. The time on your watch will maintain accuracy even in low battery mode.

After replacing the battery, you will need to perform an AC reset. After an AC reset, the second hand may skip 2 seconds for the first 10 seconds.

Seiko Caliber 8t63 Ac Reset

The original battery in the watch was also made in Japan by Seiko. The size is SR936SW which should convert to a 394 cell.


Seiko claims that the caliber 8T63 will maintain accuracy of +/- 15 seconds per month at normal operating temperatures about 41F to 95F while on the wrist.

Replacement Price:

At the time of this post, replacement prices of the 8T63 were found online in the range of $27.50 to 43.00 USD.

The 8T63 in Seiko’s Own Words:

Cal. 8T63A has a new structure employing one crown and two buttons. The construction of chronograph mechanism is based on Cal. 8R28 mechanical chronograph watch by using the one-piece 3 pointed reset hammer. While other Swiss-made watches are using separate hammers which require an assembly and adjustment of the hammers, the one-piece hammer design realizes maximum durability and stability of the component and easier maintenance. It is also equipped with the self-alignment function for all counting hands to return to zero positions instantaneously.” –source

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