The Seiko Cal. 7S26 is a mainstream automatic movement with day and date produced by Seiko Instruments Inc. (SII). It was introduced in 1996 for the popular Seiko 5 and diver model lines, replacing the 7002 family in many cases. Cal. 7S26 is very similar to Cal. 7S36 but with 21 jewels instead of 23. It is also quite similar to Cal. 7S25, introduced a decade later, which lacks the day wheel. Cal. 7S26 has been produced in Singapore, Malaysia, and Japan, and remains in production as of 2019.
Cal. 7S26 was also sold by Time Module Inc. (TMI) as Cal. NH26 at least from 2008 through 2014. In this form, Seiko specified accuracy of -25/+35 seconds per day and a power reserve of “more than 41 hours”. Seiko also specified total height as 4.90 mm.
Cal. 7S26A was the original movement, produced from 1996 through October 2006, when Cal. 7S26B was released. These feature updated parts on the balance staff, including an open-ended balance stud. It was further updated by 2011 to become Cal. 7S26C, the final version. There are many component differences between the A/B and C series movements, including the date disc and jumper, hour wheel, minute wheel and pinion, cannon pinion, oscillating weight, balance cock, ratchet wheel, first wheel, pawl lever, barrel and bridge, center wheel bridge and pinion, yoke spring, setting lever, and clutch wheel.