How to Read a Chronograph Like a Pilot
A chronograph adds a stopwatch function to a regular watch face, and its extra dials — called sub-dials or "compax" — each track a different unit of elapsed time: seconds, minutes, and often hours.
Pilots and racers used them to measure fuel burn and lap times before digital timers existed. To read one, start the pusher at the top of the case, and follow the central chronograph hand as it sweeps past the minute markers on the outer track.
The sub-dials simply catch the overflow once a full minute or hour has passed, so you rarely need to watch more than one hand at a time.