A chronograph (chrono) is a watch that incorporates an additional watch for timing intervals/events. The mechanisms are far more complex than putting & merged 2 movements into one. I am certain many chrono brands using the ST19 movement out there are either slightly lacked of proper adjustmentsor totally way-off by missing all the marks.
This is the checklist I will go through for every PerpetuaL chrono that I personally make/assemble, a very long one :
-An amplitude of a watch is like an engine's torque in car engine, should be in the range of 250-320 (unit in degrees read by timegrapher), Chinese's a bit lower 250-300 degrees. A chrono could appear to be running alright while the amplitude could be badly affected once the chrono (timing function) is deployed, the amplitude is badly compromised while the coupling wheel transmitting power by driving the chrono centered second's wheel. The worse case is the chrono function will stop by itself after a continuous running for a few hours, shorter or longer periods. When the watch is fully wound and the chrono function is "on", which will affect the amplitude inevitably, but it should just be some power reduction but no way the chrono(fully powered) will stop in less than 36 hours or even shorter time.
-The ST19 series has got up to 48 hours' power reserve (PR), with chrono function deployed the whole time, it will just affect and reduce the total PR by 1 to a few hours tops. When the watch is towards the low PR level (12 hours or less remaining) the torque is no longer strong enough to drive the chrono second wheel and therefore it could drag the watch to stop. For this ST19 or in a matter of comparison, all other chrono movements(Valjoux/Lemania/Piguet)will behave more or less the same due to the decrease in energy level. In case of a poor adjustment or no adjustment at all, a normal practice by many Chinese brands, their watches can stop if the chrono is "on" non-stop, in less than 36 hours or in many cases less than just 24.
-The running behavior of the chrono second hand, many if not observed closely, will not be running in a smooth (still in back & for motion) manner rather like jumping or hopping-like. Again it comes down to the adjustment issue or lack of one, just straight from the factory/movement supplier. In many cases, my own experience is less than 50%, the seagull factory-obtained/supplied AAA ST19 can be very well adjusted,for an absolute certaintyeach & every single ST19has to be checked thoroughly.
-The minute register, the advancement is achieved by a transmitting wheel which is commanded by the chrono second wheel to move one increment (step) by one minute's interval. Only a very proper adjustment is done, I am not gonna repeat what most other Chinese brands if not all will do or not do, can offer a precise advancement. The minute register will advance correctly just when the chrono second hand passes the 12 hr mark. Many will not even realize or don't care ? their chronos' minute registers do in fact advance at the wrong moment, either too soon or too late.
-It is easy to check if a chrono's centered hand is whether set correctly & precisely or not. A detailed visual check, better & easier with a loupe, the chrono (center) second hand must sit right at the 12 hr mark, no leaning even a bit to the left nor the right. At all times, both the chrono second hand and the minute register must always return back to their original proper & precise positions, not to the left or right. A professional’s strict & not easy setting task done to the hammer & 2 heart-shaped (second & minute) wheels of the ST19 is a "must" for such absolute certainty. Many ST19, definitely many are not, although they are marked "AAA" or you paid "AAA" price, from the day they leave the TianJin Seagull's production plant.
-In order to make that many movements everyday in seagull factory, I always find more than usual number of not so up-to-standard AAA ST19 acquired from TsinLien seagull HK branch. I of course always pay AAA (price) for AAA seagull movements if it does make any differences at all. The chrono’s settings of the second wheel, the minute register wheel & the hammer are not always done correctly. In some weird cases, the heart-shaped wheels, mostly the minute's since it's easier to manipulate, are altered very slightly (leaned to the left or right) in order to be better struck properly by the hammer thus to be achieved as if all the wheels seem to be set correctly. This kind of manipulation will lead to a faulty minute register's registrations, could be losing from a few minutes or more in one hour interval or longer interval. Not many watch fans realize this seldom discussed problem (if theirs have one) unless the chrono's registration is being checked on purpose, by another timer.
-One last check my chrono is ready to depart my work table to my customer, the chrono must be able to start to run on its own after just a few crown's turnsfrom 3,5 or up to less than 10 turns, rubs of the thumb & finger not a complete 360 revolution. If more turns are required to get it going (no shaking please) is not a good sign : balance wheel, the escapement or the main-spring.