In watchmaking, regulation is not a single operation: it's a family of technical solutions acting on different levels of the movement, with radically different objectives and tools. It's worth distinguishing them clearly, because confusing them is one of the most common mistakes even among enthusiasts.
At the deepest level there is the regulation of the oscillator. The frequency of the balance wheel is controlled by acting on inertia: the screws eccentrically mounted on the shoulders — the masselottes — shift the mass and modify the moment of inertia without touching the hairspring or the fork. This is the logic of the variable inertia balance, present both in high-end calibers and in certain mid-range movements that borrow the solution. The hairspring, for its part, has its own regulation geometry: the Breguet curve on the outside — the Phillips overcoil — and the Grossmann curve on the inside work together to make oscillations isochronous regardless of amplitude. Anyone who has seen a 216TMZ caliber on the workbench knows how difficult that geometry is to correct when someone has tampered with it without understanding it.
A level above is the fine regulation of the rate of march through the goose-neck regulator: a spring blade that restrains the regulator slide with controlled elastic pressure, preventing accidental displacements that are frequent on a straight regulator. It appears on the dial of certain contemporary watches not for vanity, but because it's a component worth showing.
Then there is the regulation of time, which includes systems very different from each other. Hacking — stopping the seconds when the crown is pulled — is the basis: it locks the balance wheel and allows synchronization to the exact second. The stop-seconds of pilot's watches is its historically most rigorous version. Quick-change of the hours allows you to move the hour hand in steps without losing the minutes reading, essential when changing time zones. The GMT caller adds an independently adjustable 24-hour hand, so the domestic reference remains unchanged. Grand Seiko's Spring Drive solves the regulation problem with completely different logic: an electromagnetic brake governed by a quartz movement slows or accelerates the tri-synchro wheel to continuously correct the rate, with a visual result — the smoothness of the seconds hand — that resembles no other mechanical system.
At the most sophisticated level are the mechanisms that protect the oscillator during regulation itself: the stopping of the tourbillon with zero-reset of the small seconds hand in the Calibre L102.1 is the most rigorous example I know. Stopping a tourbillon without damaging it requires a specially patented solution. Constant force, on the other hand, does not regulate the time but regulates the energy: interposed between the barrel and the escapement, it guarantees that the impulse to the oscillator is always uniform regardless of the spring tension.