Cal. 68A is the first of a family of ultra-thin watch movements produced by Seiko since 1969. Today these movements are reserved for the upscale Credor brand. Other closely-related members of this 6800 family include the 6810, 6830, 6870, 6890, 6898, and 6899.
The 68 family was introduced in 1969 with Calibre 68A, powering a series of ultra-thin dress watches from Daini Seikosha. The line continued with the 1973 introduction of Cal. 6810, which lasted in production for a decade. These ultra-thin watches were priced double the then-highlighted quartz models and more than four times the King Seiko and Lord Marvel lineup. By 1978, the 6810 disappeared from Seiko's catalog in favor of a line of Seiko 7820-based dress watches.
Cal. 6810 reappeared in 1991 with the 110th anniversary “U.T.D.” watch. This round ultra-thin watch used case number 6810-6000. Two years later, Seiko introduced a new line of ultra-thin automatic watches using this moment, and these remained in the catalog for the rest of the decade.
Cal. 6870 appeared in 1993 as a Credor version of Cal. 6810. It is a high-end ultra-thin manual winding movement intended to compete with similar thin calibres from Piaget, Frederic Piguet, and Jaeger-LeCoultre. All of the calibres in this family run at 21,600 A/h and measure just 1.98 mm thick. Most have 22 jewels, including cap jewels on the escape wheel, fourth wheel, and third wheel.
In 1996, Seiko introduced the skeletonized Cal. 6898, a total redesign of the movement. The balance wheel was moved opposite the crown thanks to a return to the circular shape, and the bridges were redesigned. A small-seconds version of this movement, Cal. 6898, appeared in 2005 and a two-handed version, Cal. 6890, in 2009.
Cal. 6830, introduced in 2016, is a tourbillon version of Cal. 6800. It was used in the rare Credor Masterpiece series, model GBCC999, GBCC997, and GBCC996. Seiko claims that it is the world's smallest tourbillon in terms of volume, measuring just 1.98 mm thick apart from the open heart tourbillon, which measures 3.98 mm including the carriage and 25.6 mm diameter.
The Calibre 68 family is assembled at Seiko's Shizukuishi Watch Studio in Morioka, Iwate prefecture, Japan, along with other high-end Seiko movements. It is one of Seiko's longest-running movement families.
Calibre 6810 and 6870 are roughly tonneau-shaped, measuring 19.7 mm by 16.9 mm and just 1.9 mm thick, making it one of the thinnest watch movements ever produced. By this measure, it is even thinner than the famous Piaget 9P movement of the same era. However, this measurement does not include the cannon pinion and hour wheel, so the true thickness is somewhat greater. Complete watches of just 4.4 mm were produced using this calibre, remaining some of the thinnest mechanical watches ever produced. These watches typically have a sealed case back, requiring access through the crystal and face. The face is held against the bezel with a spring rather than being screwed to the movement as is typical, so access to the movement requires removal of the hands and face.
The 6800 family uses the classical 17-jewel arrangement, with 5 extra diafix cap jewels to reduce friction. Additionally, four more jewels (not included in the official count) are arranged on the plate under the barrel. These act as a glide for the mainspring which is exposed to the base plate thanks to an open-sided barrel. This novel arrangement is just one clever trick to reduce thickness.
The pallet fork features a dog-leg bend, allowing the escape wheel to sit lower than the roller jewel. This also reduces thickness while still allowing a reasonably-sized balance wheel. The balance was also optimized, with a glued staff and integrated roller jewel to reduce thickness. It uses finely drilled holes for adjustment rather than screws of an adjuster, and the balance stud carrier is sunk into the balance cock itself rather than attached to it.
The Seiko 6800 family was used in just a few watch models
|6810||22||Tokyo stripes, rhodium plated|
|6899||26||Tokyo stripes, gold or rhodium plated, skeletonized|
|6898||Small seconds||Tokyo stripes, gold plated, voluted ratchet wheel|