Chronographs: how they work and how to use one

A chronograph is a stopwatch built into a watch that is also telling the time. Press the top pusher and a seconds hand, usually the large central one, starts sweeping. Press it again and it stops so you can read the elapsed time. Press the lower pusher and everything springs back to zero. Sub-dials count accumulated minutes, and usually hours, while a small running seconds hand tells you the watch itself is still alive.

Those three presses are the entire user interface. What differs between one chronograph and another is the engineering underneath them, and it decides how the watch feels to operate, what it costs to service and whether you can leave it running.

The three functions

Every chronograph does three things, and a mechanism is judged on how cleanly it does them.

1. Start. The chronograph wheel is coupled to the running gear train and begins to turn with it.
2. Stop. The coupling is released and a brake holds the chronograph wheel still while the watch carries on.
3. Reset (return to zero). Hammers drop onto heart-shaped cams on each chronograph arbor. Each hammer face slides down the curve of its heart, rotating it to the single position where the hammer sits flat, which is zero. Every hand snaps home at once.

The heart cam is the elegant part. It is why reset is instantaneous rather than a rewind, and why a hand that fails to land exactly on zero usually means a knocked hand or a worn hammer rather than anything deep.

The design choices you can feel

Three decisions separate two chronographs that look identical.

Column wheel versus cam

Something has to translate one pusher press into "start", the next into "stop" and the third into "reset". There are two established answers.

A column wheel is a small ratcheted wheel with vertical pillars standing on its face, like a castle turret. Each press indexes it one step, and the levers around it either drop between the columns or ride up on top of them. It is a rotary switch.

A cam system (also called coulisse-lever or shuttle cam) uses a shaped plate that slides back and forth, pushing levers with its profile. It is a linear switch doing the same job.

The honest comparison: functionally they are equivalent, and neither times more accurately. A column wheel typically gives a lighter, shorter, more precise pusher action, because the lever falls off a column rather than being pushed up a ramp against a spring. A cam usually wants more pressure and gives a more definite click. The column wheel is expensive because the wheel and its levers must be finished and adjusted individually, while a cam can be stamped.

Cam-switched chronographs are not cheap knock-offs. They are often more shock-tolerant and easier to service. If a brand charges a premium for a column wheel, you are paying for feel and craft, which is a legitimate thing to want.

Horizontal versus vertical clutch

This distinction affects how the watch behaves far more than the switching does.

A horizontal clutch swings an intermediate wheel sideways so its teeth mesh with the chronograph wheel's. Because two sets of gear teeth meet under load, the chronograph hand often gives a small stutter at the moment you start it as the teeth find each other. The mesh also loads the train, so amplitude (how far the balance swings) drops noticeably while the chronograph runs, and the rate can shift with it. The compensation is that you can watch the whole coupling work through a display back, which is why enthusiasts love it.

A vertical clutch works like a car clutch: two friction discs pressed together and released by a lever. The hand starts without any jump, and with no gear mesh to drive, the drain on the train is small and amplitude barely moves. The chronograph can therefore be left running indefinitely, which is why many modern movements use one. The cost is that the mechanism hides under a stack of discs.

An oscillating pinion, used by the Valjoux 7750, is a third route: a single pinion tilts to engage, giving a compact, robust coupling that behaves much like a horizontal clutch.

Modular versus integrated

An integrated chronograph is designed as a chronograph from the start, with the timing works on the same plate as the going train. Pusher feel is usually crisper, the case can be thinner, and the sub-dials sit wherever the designer wanted them.

A modular chronograph bolts a chronograph module onto the dial side of an existing time-and-date base movement. It is a sound, widely used approach, and it is why a great many affordable chronographs exist at all. The trade-offs are real: extra height, pushers that can feel remote because the force travels through more linkage, sub-dials set at odd depths or positions dictated by the module, and a service that means two assemblies rather than one. You can often spot one from the side, by a tall case or pushers sitting noticeably off the crown's axis.

Flyback and split-seconds

A flyback chronograph adds one behavior: while it is running, a single press of the reset pusher zeroes the hands and immediately restarts them. On a standard chronograph that takes three presses (stop, reset, start) and costs you a second or two. Flyback came from aviation navigation, where timing consecutive legs of a course without a gap actually mattered.

A rattrapante or split-seconds chronograph carries two central seconds hands on the same axis. Start them together, press the split pusher, and one freezes for you to read while the other runs on. Press again and the stopped hand instantly catches up to its partner (rattraper means to catch up), driven by its own heart cam and held by a pair of pincers while stopped. It is among the most demanding complications in regular production, because the pincers add drag exactly where drag hurts.

Reading the scales

The printed scales are not part of the mechanism. They are calculators, and they work only if you understand what they assume.

Tachymeter

A tachymeter converts elapsed time into units per hour over one unit of distance. The scale is simply 3600 divided by the elapsed seconds, printed around the bezel or the dial edge.

• Start the chronograph as you pass a mile marker, stop it at the next one exactly a mile later. If the hand stops at 45 seconds, the tachymeter reads 80: 3600 / 45 = 80 miles per hour.
• Same scale, different unit: time one kilometer and the answer is in kilometers per hour. The scale does not know or care which unit you used, only that you measured exactly one of them.
• It also works for rates. Time one item coming off a production line: if it takes 24 seconds, the scale reads 150, meaning 150 items per hour.

The limit is range. Past 60 seconds the seconds hand has gone round once and the reading is ambiguous, which is why tachymeter scales typically start somewhere around 400 and stop at 60.

Telemetre

A telemetre measures distance to an event you can both see and hear. Start the chronograph at the lightning, stop it at the thunder, and read the distance directly. Standard telemetre scales are calibrated at roughly one kilometer per three seconds of delay, so a nine-second gap reads about three kilometers, which is a little under two miles. The underlying figure, around 1,125 feet per second (343 meters per second) in air at 68F (20C), varies with temperature, so treat it as an estimate.

Pulsometer

A pulsometer is graduated for a stated number of heartbeats, printed on the dial as something like "graduated for 30 pulsations". Start the chronograph, count exactly that many beats, stop, and the hand points at the heart rate in beats per minute. No arithmetic, no counting for a full minute. Doctors' watches carried these long before anyone wore a fitness tracker.

Movements worth knowing

Three calibers come up constantly as reference points.

1969 was the year the automatic chronograph arrived from three directions at once: the El Primero, the Chronomatic Caliber 11 from a consortium including Heuer, Breitling and Buren, and Seiko's caliber 6139. Who was first depends on whether you count announcement, delivery or production, and the argument has never settled.

Living with one

A chronograph asks a little more of its owner than a time-and-date watch, and most of what goes wrong is avoidable.

Three habits protect the mechanism.

• Reset before you restart. Restarting a stopped chronograph is fine and is what the mechanism is for. Do not press reset while it runs unless the watch is a flyback: on other designs the hammers are locked out, and forcing the pusher achieves nothing.
• Do not leave it running permanently on an older or modular chronograph. With a horizontal clutch the coupling teeth stay engaged and the balance loses amplitude the whole time. A vertical clutch is built for continuous use, and some manufacturers say so explicitly. If you do not know which yours is, stop it.
• Let the hands land. A chronograph hand that misses zero is a five-minute adjustment for a watchmaker. Do not keep pressing.

Why servicing costs more

A chronograph carries many more parts than the time-and-date movement underneath it, and most are levers and springs under tension that must come out and go back in a set order. A modular design means two mechanisms. The adjustment afterwards is real work: hammer depth, the zero position, pusher travel, the eccentric that sets clutch engagement.

Expect a chronograph service to sit well above a time-and-date service, and a split-seconds well above that. Our guide to servicing and care covers what a service includes and how to judge a quote, and our complications overview maps where the chronograph sits among other functions.