Mainly designed by Tianjin Watch Factory's Chief Engineer, Mr. Zhang Zhaoli, the ST7 movement was produced from about early 1979 to 1984, and three versions have hit the market, all of them rare. There's a no-date version that looks very much like, say, a normal ST5, a mechanical hand-wind day-date version (like the gold-tone bezel variant), and an automatic day-date (the first photo and the movement). Fewer than 3500 were made.
My last photo is of my automatic day-date model. The movement rotor says 28 jewels, but the dial states 29.
I don't have the plain one.
Horological historian Joel Chan shows all three versions on his wonderful Micmicmor page:
Purchased in 2009 for $150CDN, which was the going rate at the time. Current price on Taobao: $1200+...when they show up.
(Not for sale)
Curator: Alberta Museum of Chinese Horology in Peace River; Member: China Horologe Association; Chief Expert: China Watch Overseas Working Committee (CWOWC); Sino-Canadian Horological Cultural Affairs...