05/04/2018
 4 minutes

What is the difference between a chronograph and chronometer?

By Tom Mulraney
Tudor-Heritage-Black-Bay-Black-Image-Bert-Buijsrogge

Tudor-Heritage-Black-Bay-Black-Image-Bert-Buijsrogge

If you’re new to the world of mechanical watches, you’re probably quickly discovering that there is a lot of confusing terminology to wrap your head around. Some words sound very different, but in fact refer to essentially the same thing, whilst others seem almost interchangeable and yet could not be more different.

A classic example of the latter is the whole chronograph/chronometer conundrum, made all the more confusing by the fact that a chronograph can be a chronometer and vice versa. To help clear things up for you, we’re going to explain these two different terms simply and clearly below, complete with some examples.

The best place to start is with some simple definitions of each.

Chronograph

TAG Heuer Carrera Chronograph
TAG Heuer Carrera Chronograph, Image: Bert Buijsrogge

The first thing to understand is that a chronograph is not a watch in and of itself. Rather, a chronograph is an additional function (referred to as a complication in the world of mechanical watches) that a watch indicating hours, minutes, and seconds can perform. In this instance, that function is to separately track and indicate elapsed time over defined periods. You probably know this more commonly as a stopwatch.

In a chronograph, at least one hand can be started, stopped, and returned to zero on demand to measure a duration of time to one fifth, tenth, or even hundredth of a second. Although the dial layouts of chronograph-equipped watches can vary to some degree, there will normally be two sub-counters for the minutes and hours (usually 30 minutes and 12 hours), which totalize the number of revolutions made by the central chronograph hand (which measures seconds).

A classic example of a simple chronograph is the Omega Speedmaster Professional. There are a number of variations of this model, of course, but the majority have a basic 3-6-9 layout for the chronograph displays. The 30-minute counter is shown at 3 o’clock, 12-hour counter at 6 o’clock, and running seconds at 9 o’clock, and there is a central chronograph seconds hand. There is a pusher on either side of the crown, which sits on the side of the case. The top one stops and starts the chronograph mechanism, while the bottom one resets all indicators.

Omega Speedmaster '71
Omega Speedmaster, Image: Bert Buijsrogge

That’s a simple chronograph. There are also additional variations that are more complex such as a mono-pusher, which, as the name suggests, uses a single pusher to stop, start, and reset the chronograph. A rattrapante, or split-second chronograph, allows you to time different events that begin at the same time, but do not end together. This is made possible by two chronograph hands – the second of which is called a split-second hand – that move in-sync with one another, but can be stopped independently (split) to record an intermediate time. Once the time has been read, another push on the right button causes the split-second hand to instantly catch back up to the chronograph hand. Lastly, the fly-back function enables the chronograph hand to be instantly reset to zero and immediately started again by pressing once on the chronograph push-piece.

Chronometer

A chronometer, on the other hand, is not a complication or an additional function a watch performs, though it very much sounds like one. Instead, a chronometer is the term used to denote a high-precision watch with a running seconds display whose movement accuracy has been controlled over a period of several days in different positions and at different temperatures by an official neutral body. Only mechanisms that have satisfied the criteria for precision of ISO 3159, or its equivalent, are issued with an official chronometer certificate.

In Switzerland, the certifying body is called Contrôle Officiel Suisse des Chronomètres, although it’s more commonly known as COSC. As such, a COSC-certified chronometer denotes a watch whose uncased movement has successfully demonstrated its accuracy and consistency of rate over fifteen days of tests at one of the COSC’s official testing facilities. Each watch is tested in five positions and at different temperatures and is certified as having an accuracy of -4/+6 seconds a day.

Some manufacturers have taken the concept of chronometer certification one step further. Arguably the most famous among them is Rolex, which has developed its own Superlative Chronometer certification. A Rolex movement with this title has been certified as a Swiss chronometer by the COSC and then tested a second time by Rolex – after the movement is cased up – using specially developed technology. A Rolex Superlative Chronometer watch therefore offers a precision of -2/ +2 seconds per day.

Rolex Daytona, Image: Bert Buijsrogge
Rolex Daytona, Image: Bert Buijsrogge

It shouldn’t surprise you to learn that the Rolex Cosmograph Daytona, arguably one of the most famous and sought-after mechanical chronograph watches in the world, is also chronometer certified. Well technically speaking, it’s Superlative Chronometer certified. It’s not just Rolex, however, the Panerai Mare Nostrum 42mm PAM00716 is another example of chronometer-certified chronograph, as is the new Breitling Navitimer 8 B01.

Some purists even go as far as saying that the accuracy of the times recorded can only be guaranteed if the chronograph has satisfied the criteria of the “chronometer” label, however, only about 3% of the Swiss watches made annually are COSC-certified and an even smaller percentage of those are chronographs. Whatever your view, at least now you can explain the difference between a chronograph and a chronometer with confidence.

Read more

James Bond Watches – From Rolex To Omega And Beyond

Legendary Watches: Omega Speedmaster Professional Moonwatch


About the Author

Tom Mulraney

Growing up in Australia in the 1980s and 90s, there wasn’t much of a watch scene. There was only one authorized retailer of high-end watches in the city I lived in …

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