Chronograph Watches 101: Tachymeters, Sub-Dials, and What They're For
A chronograph watch adds a built-in stopwatch function, typically operated by pushers beside the crown, with sub-dials tracking elapsed seconds, minutes, and sometimes hours, plus an optional tachymeter scale on the bezel or dial edge for calculating speed over a known distance.
Frequently Asked Questions
Do I need a chronograph if I don't time anything specific?
Not necessarily — many buyers choose chronographs for the dial's visual complexity and sub-dial detailing rather than for functional stopwatch use.
Are chronograph watches always thicker than time-only watches?
Usually somewhat, since the additional chronograph mechanism adds components beneath the dial, though the difference varies by movement design.
How the pushers and sub-dials work
The top pusher typically starts and stops the stopwatch function, while the bottom pusher resets it to zero; sub-dials display elapsed time in increments beyond what the main second hand alone could show.
A standard three-sub-dial chronograph usually tracks running seconds, elapsed minutes, and elapsed hours separately, allowing timing of events lasting minutes or hours without losing track of the base time display.
What the tachymeter scale actually calculates
A tachymeter scale converts elapsed time over a fixed distance (commonly one mile or one kilometer) into a speed reading, originally designed for calculating vehicle speed or production rates.
To use it, start the chronograph at the beginning of the measured distance and stop it at the end; the second hand's position on the tachymeter scale indicates the equivalent speed per hour.