From Chinese Watch Industry Wiki
Note: The following content is quoted in whole or in part from Wikipedia: http://en.wikipedia.org/wiki/ETA_SA
ETA SA (full business name ETA SA Manufacture Horlogère Suisse) is the largest Swiss producer of mechanical and quartz watch movements. It is a wholly owned subsidiary of the Swatch Group. The company specializes in the production of ébauche movements which are used in a number of mechanical watches. ETA has owned several important Swiss watch movement companies including Unitas, Valjoux, Peseux and Lemania, for a number of years. In fact the company is the result of successive consolidation of the Swiss watch industry. ETA manufactures quartz movements, hand wound movements and mechanical movements powered by self-winding mechanisms. Because ETA maintains vertical control over the manufacturing of all of the components required to create a watch movement (save for the hairsprings which are made by its sister company Nivarox) ETA may be considered a true manufacture.
ETA manufactures its mechanical movements only in Switzerland, however it has outsourced quartz movement and movement part manufacture to various Asian sites. Recently ETA have announced that they have ceased manufacturing in countries other than Switzerland, however quartz movements of identical design to those formerly produced by ETA Thailand continue to be made in Thailand, but without the ETA brand. From this we can infer that at least some of ETA's former foreign holdings continue to operate now as independent entities. To what extent they supply components to ETA in Switzerland is unknown.
Workhorse ETA Movements
ETA 2824-2 - ETA's basic automatic winding, twenty-five (25) jewel movement which traces its roots back to the 1950's. Available in four executions or grades: Standard, Elaborated (improved), Top and Chronometer.
Near-exact copies of the 2824-2 are produced by Sellita in Switzerland and Hangzhou and Sea-Gull in China.
In depth analysis of the ETA 2824: http://www.chronometrie.com/eta2824/eta2824.html
ETA 2892.A2 - The more upscale of the basic ETA movements, fitted with top quality components, with its design dating to the 1970's. The 2892 is an automatic winding, twenty-one (21) jewel movement, available in three executions or grades: Elaborated, Top and Chronometer. The ETA 2892.A2 is usually found in the more expensive and prestigious watches and brands. Owing to it's relatively slim height of 3.60mm, the 2892.A2 provides a good platform on which to add or build a chronograph complication.
Sea-Gull makes a near copy of the 2892.
In depth analysis of the ETA 2892: http://www.chronometrie.com/eta2892/eta2892.html
Valjoux 7750 - The ETA/Valjoux 7750 is a widely used automatic winding, twenty-five (25) jewel chronograph movement, which can be fitted with a variety of features including the triple date (day, date, month and moon phase) or a variety of two and three register models with totalizers or counters for minutes, seconds and hours. It is available in three executions or grades: Elaborated, Top and Chronometer. The traditional mechanism used in mechanical chronographs had been the Column Wheel, but with the advent of the Valjoux 7750, the column wheel was abandoned for a three (3) plane cam system (properly known as the Coulisse Levier mechanism).
Various clones of the 7750 are manufactured by the Liaoning Watch Factory and the Shanghai Watch Factory.
Unitas 6497-1 - The ETA/Unitas 6497 is a large, manual winding, seventeen (17) jewel movement, often fitted with a subsidiary (small) seconds complication in the 9 o'clock position. Originally intended for pocket watches, the 6497 has seen a recent resurgence in popularity due to its association with Officine Panerai wristwatches and homages.
Hangzhou's 9000 series is a near copy of an earlier version of the 6497/6498, whereas the Sea-Gull ST36 is closer to the current ETA version. Both Hangzhou and Sea-Gull versions are available in skeleton versions that differ from the ETA version.
Note: A thorough comparison of Sea-Gull's clone movements and their ETA counterparts can be found on the TZ-UK forum: http://www.tz-uk.com/forum/viewtopic.php?f=1&t=43661&st=0&sk=t&sd=a
Myths of Chinese ETA movements
It has been commented on various forums that ETA used to manufacture mechanical movements in China but no longer do so, and that some ETA movements on the market are assembled from residual parts stocks. There seems to be little basis for this story. ETA mechanical movement parts have only ever been manufactured in Switzerland. However there was at one time little restriction on the sale of ETA ebauches, so unassembled old stock may possibly still exist, particularly in Hong Kong.
Another related myth is that 'Asian ETA/Valjoux/Unitas' movements are made by Chinese companies using ETA tooling. A careful examination of ETA movements alongside their Chinese equivalents reveals some subtle differences. The Chinese designs appear to be adapted to simplify manufacturing and assembly and to enhance durability. There are other differences that are simply ...different. Sea-Gull, Hangzhou, Liaoning, and Shanghai watch factories have all had to create their own tooling to produce these movements.