Seiko Caliber 8S21 Watch Movement

The Seiko caliber 8S21 (aka 8S21A) is a 3-hander, no-date solar powered quartz watch movement. It has 2 jewels and is made in Japan. Seiko claims the accuracy of the 8S23 is within 15 seconds per month in normal temperatures. The capacitor for this movement is listed as “Matsushita EECW 2R4E 334”. On a full charge, this watch will provide about 120 hours of run time. There is a low power indicator that kicks in when the watch is about 15 hours away from losing power. When this happens, the seconds hand will skip, ticking 2 in 2 second intervals.

There is a similar caliber 8S23 which is the day-date version of the 8S21. Although these two movements call for the same casing diameter of 26mm, the overall diameter of the movements are different with the 8S21 being slightly larger. Keep that in mind if you’re looking to swap them.

Note: This caliber listing is still being updated, but feel free to start discussions on it in the comments below…