there were three competing chronograph movement manufacturers: Lemania, Valjoux and Venus. Venus made the popular Calibre 175 column (or pillar) wheel chronograph movement that was used in several watches in the 1940s and 50s.
Competition in this space was fierce and Venus needed money to develop newer movements so they first tried to sell their existing Cal.175 machinery and designs to the Soviet Union. The Soviets, however, already had the Strela chronograph movement (a copy of Venus’ Cal.150) which meant they weren’t interested. But the Chinese were.
Tianjin bought the Cal.175 machinery and designs from Venus and then upgraded the original 17-jewel movement to their own 19-jewel ST19 movement. They completed their second round of prototypes in 1963 and, for whatever reason, this is the year that gets added to the watch’s name when collectors outside of China refer to it. Inside of China this watch is named after the project code and is called the ‘304 Airforce chronograph’.
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