(Image credit John Davis)
The Seiko 7S26 is a low-end automatic movement mainly seen in SKX-series divers and Seiko 5 series. The series includes the 7S26, 7S36, and 7S25, which differ in an extra jewel and/or missing day complication. See this page for a detailed explanation of the submodels.
The 7S36 is the same. Details and drawings here.
Overall, I'd agree with Michael Sandler, founder of TimeZone:
From what I have seen, the 7s26 movement is a very reliable workhorse, and capable of very good performance. Their ruggedness and reliability is well-known, their basic design has been tried and proven over decades in various forms. While we now have to pay a lot more for highly finished mechanical movements, perhaps we are lucky to still have available to us very affordable mechanical watches that we can collect and enjoy.
(Quote credit is this 7005/7s26 teardown)
- Debut 1996
- Size 27mmx4.9mm, 12 ligne
- 21 jewels, Diashock
- Automatic, bidirectional winding
- Rate: 21,600 vph
- Power reserve: Appx 40 hours
- Hour, minute, central seconds, quickset day and date
- Accuracy rated at -20 to +40 seconds per day appx
- Undecorated and unadjusted
- John Davis's 7S26 review is an astonishingly good review, and one of the inspirations for WatchOtaku.
- 7005/7S26 teardown
- The 7S26 has very poor positional and isochronism. The Seiko 6R15 is better, or even the 4R.