How does a chronograph work ?

Between all mechanical watches out there, chronograph are among the most famous and desired ones. Chronograph watches (do not mix them up with chronometer!) can measure time intervals. Thanks to either innovative levers or column wheel systems, the watch can measure time on demand. While the watch still display hours, minutes and seconds, the mechanism will be able to measure elapsed time simultaneously. How is that possible?

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To run chronograph functions, watchmakers need 1) power and 2) the right seconds beat to measure accurate time intervals.

To avoid developing another system for bringing power into the watch, watchmakers have decided to get both power and the beat from the existing classic watch construction. As you know, the third gear wheel of classic mechanical watch is linked to the lever escapement, and thus provides the right beat to the entire mechanism. It’s actually with this wheel that watchmakers create the small-second function. And as you might have guessed, it’s also thanks to this gear wheel that they are going to create the chronograph.

The chronograph mechanism:
To use both the beat and power of the watch, a new gearwheel has been created and coupled with the seconds’ gear. This one called the driving wheel is actually placed on a movable arm. Thus, when the chronograph will be engaged, this arm will be pushed to the central gear (of the chrono) and will provide the right beat to the seconds hand of the chrono (basically, you put a moving gear into another static one to engage it). At this point your chronograph seconds hand is moving.
Then, by pressing a second time on the pusher you will be able to stop the seconds: this action will disengaged the driving wheel and engage a brake function to the central gear (the chrono seconds hand is stopped).
Now you can either press again the first pusher to remove the brake and engaged back the driving wheel to continue measuring time. However you can also press the second pusher and get back the chrono second hand to zero: this action will let the driving wheel disengaged, released the brake and activates little springs that get the hand back to its original position in a fraction of a second. This is the basic chronograph system for a “classic” dual-pusher chronograph.

For a mono-pusher one, the third pressure on the pusher will get back the hand to zero (you can’t start again the seconds to continue a measure).
In addition to this system, watchmakers have then added additional gears to the central one to count minutes, hours and even days (those information are usually provided on the dial with different little subdials).

To go a bit further, there are two main systems to push the movable arm by pressing the chronograph pusher : the famous column-wheel one and the less attractive but very reliable coulisse-lever one.

The column-wheel chronograph:
Column-wheel chronograph
On this picture from a 1966 Girard Perregaux calibre, the column wheel is located on the lower part of the picture. You can also recognize different types of decorations such as the côtes de Genève, circular graining and beveling.

The column wheel component is like little towers set in a circle that rotates when you press the pusher. This rotation engages the chronograph mechanism. The spaces in between the towers allow levers to fall or rise in-between the teeth, engaging functions. The colum-wheel system is therefore really safe as its shape makes functions activate one by one. One other advantage of the column wheel chronograph is that it is smoother to use. The watch owner will definitely enjoy better the column-wheel ones as the pushers are quick and smooth to use.

The coulisse-lever system (or cam and lever):
COulisse-lever chronograph
This one is set with a series of levers that are linked together by an eccentric cam. This system is cheaper to produce, easy to repair and is reliable enough for mass production. From a user perspective, this system is less smooth to use as the pressing on the pusher will be less smooth (engaging several components at the same time).

We have now covered the basics of chronograph systems. As you’ve seen, one of the main issue to resolve was the need for power. Nowadays, some watchmakers have developed new concepts to get energy that wouldn’t be using the mainspring. Researches have been done to develop other sources of energy and creating two independent systems into one watch. The idea was to 1) not disrupt the functioning of the watch (from both an accuracy and power perspective) and 2) provide an independent power reserve to operate the chronograph anytime.
Only two watchmakers are using those systems: Jaeger-LeCoultre with the Dualwing concept used in their Duomètre collection and Breguet on its Tradition line. We will cover this topic in our next article, feel free to subscribe here to get notified when we publish a new watch tip !



You can also check the accuracy of your mechanical watch on Toolwatch.io

One last thing: do you which mechanical watch measures the most accurate time?
Well it’s not El Primero with its 5hz frequency but Tag Heuer with its Mikrogirder 2000 5/10,000th of a second chronograph which has a 1’000hz frequency! It means you’ve got 7’200’000 vibrations per hour! HUGE!