Watches Anatomy of a stopwatch

Taking things a (fraction of a) second at a time


Today, we mostly rely on our various digital devices to keep time. But how did we get here? What is the model for our digital timekeeping? How does a stopwatch stop time, and with such exactitude?

It all started in the late 17th century with the “Physician’s Pulse Watch”, invented by a British horologist named Samuel Watson. This rudimentary instrument was iteratively improved upon over time, most notably by Louis Moinet in 1816, whose “compteur de tierces” measured time to within 1/60 second, and then several years later by Nicolas Mathieu Rieussec, whose chronograph literally recorded time in ink.

It wasn’t until 1916 — a solid 100 years later — that Heuer was awarded a patent for the world’s first stopwatch with 1/100 second precision. The Heuer Mikrograph was an earth-shattering advance, rendering all other “precision” stopwatches basically irrelevant. Taking preciseness to a whole new level, Heuer’s stopwatch remained an instrument at the top of its class until the advent of electronic timing in the late 60s.

While the stopwatch has changed over time, it’s basic mechanism is an established fact. If you’ve ever stopped to wonder what makes it tick, read on to get up to speed.

Stopwatch basics

The stopwatch as we know it today is a handheld timepiece designed to measure elapsed time between “start” and “stop” points. If of the mechanical or analogue variety, it is powered by a mainspring, that, like a fighter before stepping into the ring, needs to be wound up before use. 

Once wound, the mainspring is ready to, well, spring into action and start the timekeeping mechanism. The average stopwatch today has seven jewels, or jewel bearings, and its balance wheel oscillates five times per second, or at a frequency of 5 hertz. The balance wheel of an extremely sophisticated timekeeping instrument, like a vintage Heuer or a TAG Heuer Mikrograph, oscillates 100 times per second, making it an instrument of true precision.

One generally needs to push a start button, known as the “crown,” to begin recording time, and then to press that very same button to stop. Once the button is pressed, a series of at least 3 wheels (there may be more depending on how precise the timepiece is) start turning, each with varying revolution time (1 second, 60 seconds and 60 minutes). The wheels interact and record time passed since go.

Any respectable stopwatch has rate-regulating parts made of a nonmagnetic alloy that’s unaffected by temperature. Like most sensitive instruments, a stopwatch should be protected from dust and any chemical vapours (especially those of perfume) at all costs. Unlike with traditional wrist watches, the movement of a stopwatch is easily accessible through a hinged metal caseback.

Start time

Were you to open up that caseback (and dust cover) of your stopwatch at rest, you would see an unmoving balance wheel. Once you push down on the crown to start the timing cycle, the stem pushes down, rotating the star wheel and nudging something called the whip lever into action, allowing the center wheel to turn.

Stop time

Push down on the crown for a second time to stop the timing cycle. The hands freeze where they are thanks to an elegant mechanism set in motion, or rather stopped, by the stem, the push-piece, the star wheel and the trusty whip level. The chain reaction ultimately stops the balance and center wheels, and voilà, you’ve stopped time.


To set your stopwatch back at zero: one more push, either on the crown or the side button (depends on the model). The button’s stem pushes down a second spring-loaded push piece, which pivots the hammer. While pivoting, the hammer jabs two pieces of metal, sweetly heart shaped, and spins them around as if it were a dancefloor. The hearts stop when their notches reach the hammer, which snaps both hands back to zero.


Next time someone wonders aloud about wishing they could stop time, ask them if they have a second, and tell them just what that would look like, balance wheels, push-pieces and all.