The Bench · N° 29
Why Rolex and Patek use free-sprung balances
A conventional regulator changes the hairspring's active length with curb pins. A free-sprung balance leaves the spring fixed and adjusts rate by moving mass on the balance wheel.
Hen & Mills Editorial · 4 min read · 5 September 2026
The short answer is that a free-sprung balance removes one variable from the regulating system. Instead of using a movable arm and curb pins to shorten or lengthen the working part of the hairspring, the watchmaker adjusts small weights on the balance wheel.
Rolex uses its Microstella system. Patek Philippe uses Gyromax. The details differ, but both follow the same basic idea: leave the hairspring's active length fixed and change the balance wheel's inertia.
That can improve stability, but it does not make a watch accurate by itself.
What a conventional regulator does
In an indexed movement, the outer part of the hairspring passes between two curb pins. Moving the regulator changes the point at which the spring is effectively allowed to flex. That changes its active length and therefore the rate.
It is a practical system. A watchmaker can make a useful rate adjustment without removing the balance or changing the wheel itself. This is one reason indexed regulators appear in everything from inexpensive movements to very capable high-grade calibres.
The regulator is not automatically a sign of poor construction.
Why the curb pins matter
The spring does not simply stop at a single perfect point between the curb pins. It moves as it breathes, and its contact with the pins can change with amplitude and position.
The gap between the pins, their alignment and the shape of the terminal curve all matter. If the gap is too large, the effective active length can vary more than intended. If it is too tight, the spring can be disturbed or pinched.
A skilled watchmaker can set an indexed regulator very well. The free-sprung approach removes the curb-pin interaction rather than trying to perfect it.
How a free-sprung balance is adjusted
A free-sprung hairspring has a fixed outer attachment. Rate is adjusted by changing the balance wheel's moment of inertia.
Move regulating weights towards the centre and the balance can run faster. Move them outwards and it can run slower. It is similar to a skater changing rotational speed by drawing in or extending their arms, although a watch balance moves back and forth rather than spinning continuously.
Because the spring's working length is not altered during ordinary regulation, its geometry can remain more consistent.
Patek Philippe's Gyromax system
Gyromax uses small slotted weights set into the balance rim. Rotating the weights changes how their mass is distributed relative to the centre.
The weights sit within the outline of the wheel, which helps avoid increasing its outside diameter. The system also allows the balance to remain free-sprung.
The name is closely associated with Patek Philippe, but the important principle is the adjustable inertia, not the branding around it.
Rolex's Microstella system
Rolex uses small regulating nuts on the inside of the balance rim. A watchmaker turns them with a dedicated tool to change the wheel's inertia.
The nuts are normally adjusted in opposing pairs. That keeps the balance's mass distribution even while changing the rate. Moving only one weight carelessly could introduce imbalance, so regulation is a controlled process rather than a quick turn of a visible arm.
The system suits Rolex's emphasis on a robust, repeatable balance assembly.
Fine adjustment still takes care
A free-sprung balance can offer precise adjustment, but the work is less immediately accessible than moving a regulator pointer. The watchmaker needs the correct tool, the correct procedure and a clear reading of the movement in several positions.
Small changes can have meaningful effects. Adjustments must also preserve poise, which is why paired weights are moved together. A free-sprung system rewards careful regulation, but it does not remove the need for it.
What it can improve
Removing curb pins can reduce one source of variation as amplitude changes. It can also make the setting less likely to be shifted by a knock to a regulator arm.
Those are useful engineering advantages in a watch designed for consistent performance across positions and over time. They help explain why several manufacturers use free-sprung balances in movements positioned as durable or high grade.
The benefit is best understood as greater control over the oscillator, not a guaranteed number of seconds per day.
What it cannot fix
Accuracy still depends on the hairspring's shape, material and attachment. The balance must be properly poised. Friction, lubrication, magnetism, shock damage and the escapement all affect the result.
A poorly adjusted free-sprung movement can run worse than a well-adjusted indexed one. Certification and real-world performance come from the whole movement and the way it is regulated, not from this one feature.
Why many good movements retain a regulator
Indexed systems are easier and faster to adjust during manufacturing and service. They can deliver excellent results when the spring and curb pins are correctly set.
They also let a broad network of watchmakers regulate the movement with familiar tools. For a serviceable, affordable calibre, that can be a sensible choice rather than a compromise that needs an apology.
Architecture should be judged against the job the movement is meant to do.
What the owner actually gets
A free-sprung balance can offer stable geometry, good resistance to accidental regulator movement and precise inertia-based adjustment. It may also require specialised tools and more deliberate service work.
That is the real trade. Rolex and Patek Philippe did not abolish an obviously defective part. They chose a different way to regulate the oscillator, one that suits their movement designs and production systems.
The useful question is not whether a watch has a regulator arm. It is whether the complete movement keeps time consistently, can be serviced properly and has been adjusted with care.
