How a chronograph works

A chronograph is a watch with a built-in stopwatch. Alongside normal timekeeping, a separate centre seconds hand can be started, stopped and reset with pushers on the case side, while small subdials count the elapsed minutes (and often hours). The word comes from the Greek for "time writer."

The top pusher (usually at 2 o'clock) starts and stops the stopwatch function. The bottom pusher (at 4 o'clock) resets the chronograph hands back to zero once stopped. The crown between them still winds the watch and sets the time as normal.

The column wheel is a small castle-shaped wheel that coordinates the start, stop and reset levers — each pusher press turns it one notch, and its columns raise or drop the levers in the right order. It is the traditional, more expensive way to control a chronograph, prized for its crisp pusher feel. Simpler movements use a stamped cam instead, which works just as reliably but feels less refined.

It does no harm mechanically — the chronograph gears are designed to run — but on most movements it noticeably increases power draw, so an automatic may run down faster off the wrist and amplitude can drop slightly. Most owners run it only when timing something.

They sound alike but mean different things. A chronograph is a function: a stopwatch built into the watch. A chronometer is a certification: a movement that has passed independent accuracy testing (such as COSC's −4/+6 seconds per day). A watch can be both, either, or neither.

The tachymeter — the numbered scale on many chronograph bezels — converts elapsed seconds into units per hour. Start the chronograph at a mile marker and stop it at the next: the number the seconds hand points to is your average speed in mph. It works for anything measured per hour, not just speed.