In 1960s Switzerland there were three competing chronograph movement manufacturers: Lemania, Valijoux and Venus. Venus made the popular Calibre 175 column wheel chronograph movement that was used in several watches in the 1940s and 50s.
In 1961, the Chinese Government assigned the task of developing and producing an air force chronograph for the Army to the Tianjin-Seagull Watch Factory.
Seagull bought everything from the Venus company, the machines, blueprints etc. that was used to produce the Venus 175 and then upgraded the original 17-jewel movement to their own 19-jewel ST19 movement.
By 1965 these watches had met all the requirements and passed all the Ministry’s tests so an order was placed. In 1966 Tianjin-Seagull delivered 1,400 of these watches to the air force.
Inside a mechanical chronograph, you’ll usually find one of two types of movement; a column wheel movement or a cam-actuated variety.
Seagull ST19 is based on a column-wheel system, like Patek Philippe CH-29-535 movement and Zenith El Primero watch.
When you push the “start” button you act on the column wheel operating lever which moves the wheel. That then moves the clutch rocker away from its detent. The rocker then engages with the oscillating pinion with the chronograph wheel and the hand starts moving. Click to stop and the column wheel turns the other way.
A cam and lever has – near enough – the same number of parts as a column wheel set-up, but it costs rather less to produce as the tolerance of the parts doesn’t need to be quite so precise. Cam-actuated system is used on ETA/Valijoux 7750 movement. When you push the “start” button you act on a level and an oscillating pinion that moves on the chrono wheel.