Chronometer pocket Watch
We often hear the terms "chronograph" and "chronometer" used inaccurately or incorrectly, so let's clear up the confusion by taking a closer look at what makes a watch a chronograph or a chronometer.
The word "chronograph" combines the greek words for time ("chronos") and writing ("graphos")... it literally means "time-writer". So by definition, a chronograph is just a device for marking or recording a time interval. The earliest "time-writers" actually made a mark on paper with ink to mark the beginning and end of some event, thus allowing the calculation of elapsed time.
Louis XVIII is said to have commissioned the construction of a marking-timer for horse-racing in 1821, and its maker, Nicolas Mathiew Rieussec, is thus credited with the creation of the first "commercial" chronograph. In fact, Louis Moinet had created a timer for astronomical observations at least as early as 1816, so Rieussec may not be the rightful "inventor" of the chronograph. Another key development occured in 1844, when Adolphe Nicole developed a chronograph with a resetting mechanism, allowing successive interval measurements. Most of the mechanical chronographs developed over the past 100 years use some variation of Nicole's "start-stop-reset" mechanism.
Today, the term "chronograph" commonly refers to a watch that has an interval timer built into it. The chronograph mechanism is probably the most popular "complication" found on higher-grade mechanical watches. Whether it's the additional sub-dials and pushers, or the intricate complications of the mechanism, the mechanical chronograph has an unmistakable cachet in the world of watches. Today most chronographs take the form of a wristwatch, but there are many fine examples of vintage chronograph mechanisms in pocket watch form.
Waltham chronograph. 14-size, Model 1884, split-second, 15-jewels, gold-train, gold escape wheel.
Operation of the Chronograph
Chronograph watches today can be broadly classified as one of three types: simple, flyback, or rattrapante.
A typical simple chronograph has two buttons, or "pushers" associated with the operation of the chronograph mechanism. The usual operation of these buttons is as follows: press the first button once and the timer begins running, press the first button again and the timer stops running, press the second button once and the timer indicator(s) return to their zero position. During all timing operations, the watch continues to run as usual. With a simple chronograph, it requires 3 button-presses to start-stop-reset the chronograph timer.
When the timer is running, one of the hands (usually the "sweep" second hand) will move around the dial to measure seconds. Every time the seconds hand goes around the dial, one of the sub-dials will record the passage of minutes. On some chronographs, there is even an additional sub-dial which records elapsed hours. While this is the "typical" chronograph arrangement, it should also be noted that there are many special-purpose chronographs designed to be useful for a specific application (navigation, scuba-diving, aviation, auto-racing, etc.)
Chronographs often have a complicated-looking scale on the bezel with lots of little numbers and markings. Many chronograph bezels are marked to function as a tachymeter, which allows for calculation of speed over a given distance, or distance based on speed. Tachymeter bezels were very popular with aviators and race-car enthusiasts, because they allowed for rapid time/distance calculations. Most early tachymeter bezels were fixed, but in 1958 Heuer introduced the rotating tachymeter bezel, which allowed additional timing calculations to be performed.
Another common chronograph bezel is the telemeter, which allows calculation of distance to an observed event. For example, if you start the timer when you see a flash of lightning, and stop it when you hear the thunder, the telemeter scale will indicate the distance to the flash.
Flyback and Rattrapente
A "flyback chronograph" is a more advanced chronograph which provides for a near-instantaneous reset and restarting of the timer function while it is running. A single button or pusher actuates the stopping, reset to zero, and starting of the second hand.
A "rattrapente chronograph" or "double chronograph" as they are sometimes called... comes from the German word for "split-seconds." A rattrapante chronograph has an additional seconds hand that is exactly aligned with the primary second hand. This additional second hand can be stopped independently to record the timing of splits, or multiple events occuring simultaneously, e.g. multiple runners in a race.
Mechanical Chronograph Repair
Chronographs, whether vintage or modern, can be extremely complicated mechanisms, with hundreds of small parts which must all operate and interract correctly. There are several critical adjustments which must be made correctly if the chronograph is to function properly, and we find these adjustments are often made badly by a well-intentioned watchmaker who doesn't really have a clear understanding of the chronograph mechanism and "gets in over his head".
Mechanical chronograph repair, especially for rare vintage chronographs, can be an understandably time-consuming and expensive undertaking, but there's something really cool about wearing or carrying a high-quality vintage chronograph. From a watchmaker's perspective, few tasks in the world of horology are as satisfying as bringing one of these wonderful little machines back to life.
So now you know that the term "chronograph" refers to specific interval-timing functionality that's built into the watch. The term "chronometer", on the other hand, is all about how the watch performs as a timekeeping device.
In order for a modern watch to be called a chronometer, it must be certified as to its timekeeping performance. The certification of Swiss chronometer watches is done by COSC, or Contrôle Officiel Suisse des Chronomètres. COSC is a non-profit organization funded by the Swiss watch industry, and is the official certifying body for all Swiss-made chronometers. Chronometer watches are tested for precision and accuracy under a wide range of conditions, and only watches which meet or exceed all standards are awarded the chronometer certification.