What a tourbillon does in a wristwatch, and what it doesn't

The tourbillon is the best-known word in haute horlogerie, and probably the most overrated. The mechanism is more than two centuries old, it is difficult to make, and it is lovely to watch. But the problem it was invented to solve is one a wristwatch barely has.

The trouble with pocket watches

The heart of a mechanical watch is the balance: a small wheel that swings back and forth on a hairspring, usually several times a second. As long as each swing takes exactly the same time, the watch keeps good time. In practice it doesn’t. A balance is never perfectly poised, and nor is the hairspring. When the watch hangs upright, gravity pulls on that tiny excess weight, and depending on where it sits, the watch runs slightly fast or slightly slow.

For a pocket watch, that was a real problem. It spent much of the day in the same position in a waistcoat pocket, crown up. An error that occurred in that position therefore added up in the same direction, day after day.

Breguet’s answer

In 1801, in Paris, Abraham-Louis Breguet was granted a patent for a solution that did not remove the problem but averaged it out. He mounted the balance, the hairspring and the escapement together in a small cage that rotates, usually once a minute. The error caused by gravity still occurs, but in a position that is constantly changing. What runs fast in one position runs slow half a turn later, and over a minute the two largely cancel out.

It is an elegant idea, and it comes at a price. The cage has to be light, because the movement has to turn it all day long, and it has to be precise, because any irregularity in its rotation disturbs the timekeeping all over again. A tourbillon cage easily consists of dozens of parts, and finishing them is handwork.

On the wrist

A wristwatch does not hang in one position for hours. It lies flat on a desk, stands upright while you type, tilts as you walk and turns whenever you move your hand. Its position is changing all the time anyway, so gravity already averages itself out to a degree. What the tourbillon adds is smaller than in a pocket watch.

On top of that, a modern movement suffers less from many of the original causes. Hairsprings made from modern alloys or silicon are more consistent than those of Breguet’s day, balances are poised more finely, and good manufacturers regulate a movement in several positions. A well-adjusted watch without a tourbillon can therefore keep better time than a poorly adjusted watch with one.

That does not mean a tourbillon on the wrist has no effect at all. In the positions where the watch stands upright, it still averages out the error. But if you buy a tourbillon in search of a more accurate watch, you are mostly paying for something else.

What you are paying for instead

Craftsmanship, first of all. Making, finishing and regulating a tourbillon well is one of the hardest tasks in watchmaking, and it shows. On most models the cage sits behind an aperture in the dial, so you can watch the mechanism turn.

There are variations that show how makers have kept playing with the principle. The flying tourbillon, devised in 1920 by Alfred Helwig at the watchmaking school in Glashütte, has no bridge on top: the cage is supported only from below, so it appears to float. The karrusel, patented in 1892 by the Dane Bahne Bonniksen, works on the same idea but is driven differently, and usually turns far more slowly. There are also cages that rotate about more than one axis, to cover the horizontal positions as well.

The verdict

The tourbillon is an invention that has outlived its original purpose. In a pocket watch, it solved a real problem. In a wristwatch, it is above all a demonstration of what a maker can do, and that is a perfectly good reason to want one. It is simply not a reason to assume the watch will keep better time.

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This is a demonstration article. It shows the layout of a feature. The technical explanation is common knowledge, but has not been checked against the sources again before publication.