Some Seiko Calibres 7S Series CalibresThese are the most prolific mechanicals produced by Seiko, and incidentally they are the only Seiko mechanical regularly imported into the US by Seiko USA. Technically the 7S calibres are very simple and efficient bi-directional winding automatic movements that have no provision for handwinding. The 21 jewel 7S26 is the most common variant, found from the US to Malaysia.
Les common is the 23 jewel 7S36 which is generally only seen in Japan, though occasionally encountered in western markets. I suspect that the two extra jewels are for the auto-winding gear train. Both 7S calibres run at 21,600 vph, have day and date displays, and have a flat matte, nickel-plated finish. Unlike the rest of Seiko's mechanical movements, the 7S26 is primarily manufactured outside of Japan by a subsidiary in Singapore, though some - particularly the 7S36 variant - are manufactured in Japan, as is the 7S55, the final and rarest member of the 7S family. The 7S55 has only been used in a single collection of watches exclusive to Japan.
4S Series CalibresFirst introduced in 1992, the 4S calibres make up the "bread and butter" of Seiko's mechanical movements. They are a diverse group of automatics and handwinds which are actually based on a single Seiko ebauche. It should be noted that all Seiko automatics above the 7S level can also be wound by hand.
The base movement of the 4S series is the 4S15 a 25 jewel automatic with center seconds and date calendar. It runs at 28,800 vph, has a flat brushed finish except for the rotor which is finished with colimaconnage, is nickel-plated, and has cap jewels on both the escape and fourth wheels -- a nice touch which dates back to the early Seiko "Chronometers" which often featured cap jewels all the way to the center wheel. The use of colimaconnage is also a Seiko tradition that dates back to the Grand Seiko automatic movements of the 1960s. The 4S15 is essentially a reissue of their 52 series calibre from the 1970s, originally used in their premium King Seiko line. It is probably the highest quality simple automatic movement at this price point in the world (35,000 to 45,000 Yen). Calibre 4S12 is a variant of the 4S15 with an additional 24-hour GMT hand.
The basic 4S handwind, calibre 4S24, is a 21 jewel center-seconds movement. Simply put, it is calibre 4S15 with the automatic winding removed (akin to the relationship between Blancpain calibres 1161 and 1106). In removing the rotor and winding gears, the simple three-bridge top plate of the 4S15 is further simplified into a two-bridge 3/4 plate architecture. It has a simple flat matte and rhodium plated finish. Calibre 4S28 is a 24 jewel version of 4S24 with indirect subsidiary seconds indication. Finally, the 4S79 in a 29 jewel variant with indirect subsidary seconds and power reserve indication.
The 4S7x series was first introduced in 1995 for Seiko's mechanical luxury watches and is comprised mostly of automatic movements based on the 4S15. The basic movement is the 25 jewel calibre 4S71, with center seconds and no date. Calibre 4S77 adds a date subdial, retrograde day display, 24 hour GMT subdial, and three jewels. Calibre 4S79 adds a power reserve indicator, small seconds display, and four jewels. The only handwind, calibre 4S79A, is a 31 jewel certified chronometer with power reserve and small seconds display based on the 4S29. The automatic movements have a colimaconnage and gilt finish, and the handwind is finished with "Tokyo Stripes" and is also gilt.
6S Series CalibresLaunched in 1998, the 6S calibres are Seiko's three-register column wheel chronographs, both automatic and handwinding. Calibre 6S78 is a 34 jewel automatic chronograph with date calendar. At 7.2mm thick and 28.4mm in diameter it is a robust movement. The 35 jewel hand-wound calibre 6S74 has no date calendar but adds a power reserve display, and the 40 jewel automatic calibre 6S77 has both the power reserve display and calendar date window. The automatic movements in this series are finished with brushing on the plates and colimaconnage on the rotors, and the manual-wind is finished with Tokyo Stripes. Calibre 6S99 is the skeletonized version of calibre 6S74. All four movements are gold-plated. Calibre 6S37 is a recent variant of calibre 6S77 which is rhodium plated rather than gilt.
68 Series CalibresThe 68 series is comprised entirely of thin hand-wound movements. Calibre 6810 is a 22 jewel tonneau-shaped calibre, finished with Tokyo Stripes and rhodium plating. First seen in 1993, calibre 6870 is a 21 jewel movement with only hour and minute indications. Based on the earlier 6870, ultrathin calibre 6898 is 1.98mm thick -- thinner than Piaget's ultrathins, but thicker than those of Jaeger-leCoultre and Frederic Piguet. The 6898 is finished with Tokyo Stripes, gold-plating, and a voluted ratchet wheel. Indirect small seconds display adds 5 jewels for a total of 26. Calibre 6899 is the skeletonized and engraved version of 6898 -- available gilt or rhodium plated. The 68 calibres run at a 21,600 vph beat rate, and all feature cap jewels on the escape, fourth, and third wheels.
9S Series CalibresThe premium simple automatic calibre of Seiko's mechanical collection, 9S production is limited to 300 units per month -- a tiny number for a manufacture that makes over 30 million watches per year. The 9S series centers around very robust simple automatic movements built on the same scale as Rolex's 31xx series calibres. The 26 jewel calibre 9S55 is 5.3mm thick and 28.4mm in diameter, with center seconds and calendar date indication. The 24 jewel calibe 9S51 is simply a 9S55 without date window. The 20 jewel 9S54 is a hand-wound variant with center seconds and no date function, featuring a split 3/4 top plate. All 9S movements are finished with Tokyo Stripes and rhodium plating, and are adjusted to six positions.
8L Series CalibresThe 8L75 is an unadjusted and more simply finished variant of the premium calibre 9S55 (akin to the relationship between Chopard's LUC 3.96 and 1.96). It has a brushed and gilt finish, with colimaconnage on the rotor. The final 9S55 variant is calibre 8L35. Like the 8L75 it is unadjusted, but rhodium plated rather than gilt. The last member of the 8L family is calibre 8L34, a variant of calibre 9S54. With no change in jewel count, the 8L34 features subsidary seconds rather than central seconds.
Looking ForwardOn November 17th of 1998 Seiko received a patent for new handwound tourbillon calibre with an offset screwed balance wheel (like the Blancpain calibre 23). The tourbillon cage upper plate which bridges the balance and escape wheel is shaped as a monogram "S." An unusual factor of the cage design permits adjustment and regulation with the cage assembled, using a special jig. Conventional tourbillons must be disassembled for any adjustment of accuracy -- a large factor of the great expense of tourbillon watches. The cage is also an ultrathin design, attempting to circumvent the bloating common to most tourbillon calibres.
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