Many watch enthusiasts never dare open their watch's case, terrified at the thought of damaging the heart of the mechanism. Yet correcting the gain or loss of a mechanical movement is a fascinating operation, entirely accessible with the right method — provided you know exactly where to place your tweezers.
Understanding what you are actually regulating
A mechanical watch does not "slow down" because it is tired: it beats at a frequency imposed by its regulating organ, the balance-spring pair. This frequency (2.5, 3, 4 or 5 Hz depending on the calibre) depends directly on the active length of the balance spring. Regulating accuracy means altering that active length — not touching the balance wheel itself, and certainly not the mainspring barrel or the gear train.
A shorter spring speeds up the oscillations: the watch gains. A longer spring slows them: the watch loses. The whole operation hinges on the infinitesimal movement of a single slider: the regulator index.
The regulator index: the gain-loss slider
The regulator index is a small steel part mounted on the balance cock, fitted with two tiny pins through which the outermost coil of the spring passes. Moving it one way shortens the spring's active portion (marked "+" or "A" for advance), moving it the other way lengthens it ("–" or "R" for retard). On modern calibres fitted with an ETA 2824 or Sellita SW200 balance cock, a light push suffices; on an older movement, the rounded tip of a brass tweezer is used so as not to scratch anything.
The movement is measured in fractions of a millimetre. A timing machine (Witschi, Timegrapher 1000) makes the adjustment precise: the aim is 0 s/d dial-up before fine-tuning the other positions.
If you have never held a timing machine, the regulation chapter of our guide on how to learn watchmaking online walks through the readings step by step, and the watchmaking for beginners path shows which gestures to master first.
The touch: gentleness, support, breathing
Rest your elbows on the bench, breathe, brace your little finger on the movement holder. Bring the brass tweezer in at an angle, never vertically above the spring. You do not push the index: you caress it. Between each micro-adjustment, check again on the timing machine before touching it once more. The golden rule: never two corrections without a measurement in between.
What must never be done
Never touch the spring itself — warping it by a hair's breadth is enough to ruin isochronism. Never dismantle the balance "just to see." Never attempt regulation on a dirty watch: a movement lacking oil or with a fouled escapement is not to be regulated but overhauled. Finally, do not confuse gain-loss (regulator index) with amplitude (cleaning, mainspring energy, escapement play).
Frequently asked questions
Can you regulate an automatic watch yourself?
Yes, provided you have a suitable case-back opener and a timing machine. On calibres with a free regulator index (such as the ETA 2892), the adjustment is direct; on screwed balances (Rolex, Patek), it is best left to a professional.
What amplitude should you aim for after regulation?
On a well-maintained modern movement: 270°-310° dial-up, with an acceptable drop of ≤ 40° between positions. Below 220°, the watch needs a full overhaul, not a simple adjustment.
How long should you observe it before drawing conclusions?
At least 24 hours on the movement holder in each position, ideally 48 hours. The average rate is calculated cold, once it has stabilised.
Ready to take your first steps at the bench? Discover the Décalibre curriculum and learn to regulate your first calibre with confidence, thanks to our interactive macro videos.