What is a tourbillon?

How it works

A mechanical watch keeps time with its balance wheel, which swings back and forth several times a second. Gravity pulls slightly on the balance and hairspring, and the effect changes depending on which way up the watch is held, so a watch runs at slightly different rates in different positions.

A tourbillon mounts the whole regulating system, the balance, hairspring and escapement, inside a small cage that rotates continuously, usually once a minute. Because the cage keeps turning, the positional errors average out instead of adding up.

Most tourbillons are visible through an opening in the dial, and the rotating cage is the reason most people buy one. A flying tourbillon is supported from one side only, with no bridge across the top, so the cage appears to float.

History

Abraham-Louis Breguet patented the tourbillon in 1801 for pocket watches, which spent all day upright in a waistcoat pocket, so the same positional error accumulated hour after hour. Alfred Helwig developed the flying tourbillon in 1920. Wristwatch tourbillons became a showcase of high watchmaking from the 1980s onwards.

Before you buy

On a wristwatch, which changes position constantly as you move, a tourbillon's accuracy benefit is small, and a well-adjusted ordinary movement can match it. People buy tourbillons for the craftsmanship and the spectacle. Swiss tourbillons usually cost tens of thousands of dollars; Chinese-made tourbillon movements sell for a fraction of that.

Questions

Does a tourbillon make a watch more accurate?

In a pocket watch, yes, measurably. In a wristwatch the benefit is debated, because your arm already moves the watch through many positions. A tourbillon today is mostly a demonstration of skill.

Why are tourbillons so expensive?

The cage is made of dozens of tiny parts that must be extremely light and perfectly balanced, and the whole assembly is hand-finished and adjusted. Few watchmakers can make one, so Swiss tourbillons rarely cost less than five figures.