Why Are Mechanical Movements So Susceptible to the Effects of Gravity?

There is something profoundly impertinent about mechanical watches. A few grams of brass, steel, synthetic ruby and hairspring attempt to measure time with regularity while constantly resisting the Earth’s pull. Gravity—the force we forget until we drop a glass, our knees give way, or we have to haul ourselves out of bed the morning after a night of excessive drinking—is one of the great adversaries concealed within a mechanical movement.

Gravity does not break a watch. Nor does it visibly slow it down, as a violent shock or magnetic field might. It acts more subtly, like an aesthete with a fondness for disorder. It alters friction, disrupts the balance’s oscillations, affects the position of the hairspring and creates rate variations depending on whether the watch is resting dial-up, crown-down, on its side or on the wrist. In other words, it reminds the watchmaker of one simple truth: in a mechanical watch, precision is never given. It must be earned.

Gravity, the silent enemy of watch accuracy

A mechanical movement operates through an almost absurdly elegant chain of energy. The mainspring unwinds inside the barrel, transmitting its energy to the gear train, which drives the escapement. At the end of that chain, the balance and hairspring oscillate. This is the heart of the regulating system. It is the balance that sets the rhythm.

In the mathematical ideal, the balance would oscillate perfectly in every position, maintaining the same amplitude, with unchanged friction, no additional loads, constant lubrication and no microscopic imperfections in its components. In the real world—the world of watchmaking—not one of these conditions exists.

Gravity acts primarily on the movement’s most delicate components: the balance, the hairspring, the bearings and the escapement. Its effect varies according to the watch’s position. A watch resting dial-up does not experience the same loads as one resting crown-down. And the human wrist has the unfortunate habit of moving in every conceivable direction, quite regardless of chronometer standards. Things become complicated very quickly.

Positions as a small theatre in which a watch reveals its character

When a watchmaker regulates a watch, they do not simply rotate it on the bench and nod with satisfaction. The rate is measured in several positions: dial-up, dial-down, crown-up, crown-down, crown-left and crown-right. These correspond to the positions a watch may occupy in daily life, particularly when it is not being worn.

Why are positions so important? Because friction at the pivots changes. In horizontal positions, such as dial-up or dial-down, the balance pivots meet the jewels differently than they do in vertical positions. In a vertical position, the effect of the balance’s own weight becomes more pronounced. Even the slightest imbalance can cause the oscillations to speed up or slow down.

This explains why a watch may gain two seconds a day on the wrist, lose six seconds on the nightstand and return to a respectable rate in another position. It is not being capricious. It is being mechanical.

Amplitude, beat and friction

Amplitude refers to the angle through which the balance travels during each oscillation. A properly regulated watch will generally show a high and stable amplitude, although the precise figure depends on the calibre, the state of lubrication and the architecture of the movement. When gravity alters friction, amplitude changes too. And when amplitude changes, the rate can change with it.

The balance is not the only factor. The pivots—the minuscule end sections of the staff—operate inside ruby jewels. If the oil has deteriorated, migrated or distributed itself differently according to the position, gravity magnifies the discrepancy. At this scale, a drop of lubricant becomes a landscape. Dust becomes a boulder. Watchmaking is geography for insects.

The hairspring, a metallic strand of hair at gravity’s mercy

The hairspring is one of the most captivating components in a mechanical watch. Depending on the calibre, it is made from an extremely fine metal alloy or silicon, repeatedly contracting and expanding with each half-oscillation of the balance. Its purpose is to return the balance to its neutral position while maintaining the greatest possible regularity.

The problem is that the hairspring is also a physical object. It has mass, shape and points of attachment. Its breathing motion may be very slightly eccentric. In a vertical position, its own weight can marginally compromise its concentricity. For centuries, watchmakers have sought to improve this breathing motion through hairsprings with terminal curves. The most famous remains the Breguet overcoil. By raising the outer end of the hairspring, Abraham-Louis Breguet achieved a more concentric expansion and contraction, and therefore greater stability.

We sometimes forget that such refinements are not intellectual adornments intended to fill a catalogue. They are answers to extremely concrete problems. Gravity pulls, metal resists and the watchmaker finds a compromise.

A brilliant answer to a very old problem: the tourbillon

Any discussion of gravity must include the tourbillon. Patented by Abraham-Louis Breguet in 1801, the mechanism was conceived for pocket watches. At the time, a pocket watch spent most of its life vertically oriented inside a waistcoat pocket. This constant position amplified gravity-induced errors in the regulating system.

The tourbillon is easy to explain but difficult to execute. The balance, hairspring and escapement are housed in a mobile cage, which generally completes one rotation per minute. Rather than allowing the regulating system to experience gravity in the same direction at all times, the cage successively exposes it to every vertical orientation. The errors therefore tend to cancel one another out.

For pocket watches, the idea made considerable sense. With modern wristwatches worn on constantly moving wrists, the discussion becomes rather more nuanced. The tourbillon remains a magnificent feat of horological engineering, but its practical chronometric benefit depends on the calibre, regulation, quality of finishing and conditions of use. In other words, a tourbillon watch is not automatically more accurate than a finely regulated, chronometer-certified three-hand watch. My apologies to anyone who has made this argument at a dinner party.

A few remarkable tourbillons

Even so, certain tourbillons have left a lasting mark on the history of the modern wristwatch. The Audemars Piguet Référence 25643, introduced in 1986, is often cited as the world’s first serially produced automatic tourbillon wristwatch. Slim, daring and technically outstanding, it raised a question that watchmaking has continued to revisit: do complications exist to solve problems, or to demonstrate that they can be solved with extravagant methods?

At Breguet, tradition naturally remains central. Each Classique Tourbillon model pays tribute to the original invention while incorporating contemporary materials, finishing and construction, depending on the reference and specification. Prices vary substantially, but models in precious metal with extensive complications can readily exceed €100,000 on the new-watch market.

The carrousel: less famous, but every bit as serious

The carrousel is often described as the tourbillon’s cousin. Invented by the Danish watchmaker Bahne Bonniksen at the end of the nineteenth century, it pursues a similar goal: correcting positional variations caused by gravity. Its construction, however, is different. Whereas a tourbillon generally uses the same power source for the rotation of the cage and the escapement, the carrousel employs a more complex independent drive system.

For a long time, it was regarded as a more robust solution and, in some circumstances, one that was easier to regulate. It is far rarer in contemporary production, however. Blancpain brought renewed attention to the mechanism by incorporating it into remarkable watches, particularly in the Le Brassus collection, sometimes even combining it with a tourbillon. Clearly, one anti-gravity device was not enough to soothe the human ego.

Modern solutions: silicon, high frequency and fine regulation

The struggle against gravity is not limited to rotating cages. Some of the most decisive advances are concealed in components that are considerably less theatrical.

Silicon, for example, has transformed the manufacture of regulating and escapement components. Lightweight, highly non-magnetic and exceptionally precise geometrically, it makes it possible to produce hairsprings whose form is controlled with extraordinary accuracy. Several maisons, including Breguet, Omega, Patek Philippe and Ulysse Nardin, have explored this path according to their own philosophies. Patek Philippe’s Spiromax hairspring and the silicon hairsprings used by Omega in its Co-Axial Master Chronometer calibres are part of a broader pursuit of overall stability.

High frequency offers another answer. Movements operating at 36,000 vibrations per hour, such as certain Zenith El Primero calibres, divide time into finer increments than movements running at 28,800 vibrations per hour. This can improve rate stability in response to certain disturbances, but it does not make the watch immune to gravity. Nothing completely liberates a mechanical watch from gravity. Not even price. That can sometimes be the most painful discovery of all.

Finally, there is regulation. Real regulation. The watchmaker adjusts the regulator or the eccentric weights of a free-sprung balance, checks the reference positions, measures positional variation, corrects it and starts again. Thorough regulation in five or six positions can have astonishing results. It may be less glamorous than watching a flying tourbillon rotate beneath sapphire crystal, but in everyday life it is usually more useful.

Why a watch gains or loses time at night

Every enthusiast has noticed it at least once. The position in which a watch rests overnight affects its rate. A watch that gains on the wrist may lose a little when placed crown-up. Another may perform better dial-up. There is no universal rule because every movement has its own positional variations.

This allows gravity to be used as a practical, experience-based tool. If your watch consistently gains, try leaving it in several different positions over the course of a few nights and observe the results. There is no need to turn the bedside table into a COSC laboratory. A little method is all that is required.

Experienced collectors know this small ritual. Resting a watch in a position that slightly offsets its gain or loss is a simple way of entering into dialogue with the movement. You can never completely own a mechanical watch. That is something we learn over time.

COSC, METAS and the reality of accuracy testing

Chronometer certifications exist precisely because accuracy must be verified under a range of conditions. COSC, the Swiss Official Chronometer Testing Institute, tests the movement on its own for 15 days, in several positions and at different temperatures. The commonly quoted tolerance for a mechanical movement is −4 to +6 seconds per day.

For the Master Chronometer certification issued by METAS, Omega tests the finished watch after casing. Among other things, it verifies resistance to magnetic fields and checks the rate in several positions and at different levels of power reserve. Rolex, meanwhile, states a tolerance of −2 to +2 seconds per day for its cased Superlative Chronometer models, according to its own internal standards.

These figures do not eliminate the effects of gravity. They show that the watch has been designed, manufactured and regulated to control those effects within a defined range. That is the difference between a promise that sounds like magic and industrial discipline.

Does gravity explain everything? No—and thankfully so

How convenient it would be to blame every rate deviation on gravity. Too convenient. The rate of a mechanical watch can also be affected by magnetism, shocks, wear, degraded lubricants, insufficient power reserve, a sticking or distorted hairspring and a poorly adjusted escapement. Gravity is a leading actor, but it is not the only culprit.

In older watches, positional variation may become more pronounced when the bearings are worn, the oil has dried or the balance has lost some of its equilibrium. In high-quality modern watches, it is often restrained, but never eliminated entirely. No machine is perfect. Besides, such a machine would probably be rather boring.

What gravity really teaches us about mechanical watches

The susceptibility of a mechanical movement to gravity is not a weakness to be ashamed of. It is a condition of the mechanical watch’s existence. A mechanical watch is an object regulated to resist the real world: weight, friction, temperature changes and the unconscious movements of its owner. It is not fascinating despite its fragility, but because it strives for precision while carrying that fragility within it.

Quartz solved the problem of everyday accuracy with almost brutal efficiency. Smartwatches make the contrast even sharper. They synchronise with atomic clocks while your tourbillon meditates inside its cage. And yet we return to mechanical movements because their effort is made visible. Because they transform physical constraints into architecture, regulation and invention.

Gravity pulls everything downwards. Watchmaking responds with bevelled bridges, breathing hairsprings, rotating cages and stubborn balances. This is not merely a battle over a few seconds a day. It is an elegant act of defiance.