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FROM THE BENCH: Regulation 3 — Practical Applications

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FROM THE BENCH: Regulation 3 — Practical Applications

We talked about positional accuracy several times in the other two articles about regulation, so let’s dive into that concept.Sellita SW330-1 during measurement on a timing machine

Positional accuracy is important because a watch’s rate will vary as it moves around; unlike a clock, which is bolted to the wall, watches are constantly in motion, and the balance is affected by its relationship to the ground by gravity.

Typically, a balance will keep relatively similar time in its “dial positions,” which is when the watch is dial-up (wrist toward your face) or dial-down (wrist turned away from your face). In these positions, the balance and hairspring are parallel to the ground and relatively unaffected by gravity. The balance is also rotating on the tip of its staff (axle), which is a rounded pivot that rests on a perfectly-polished ruby jewel—very low friction.

Watch in "stem left" position at a desk
Unless your watch is spending its whole life on the nightstand, it will spend lots of time in the “pendant” or “stem” positions. This is when the stem is pointing in different directions, typically down (watch at your side), left (sitting at your desk), and up (reaching overhead). Stem right doesn’t happen much unless you’re scratching behind your ear (or wearing the watch on your right wrist).

These different positions will vary from each other, and can vary from the dial positions as well. In the stem positions, the balance and hairspring are perpendicular to the ground, so gravity has a greater effect, and the balance is moving on the side of its axle, which has more friction than the tip.
Vintage pocket watch adjustment engravings
Correcting for these variations is called “adjustment,” and if you see a movement advertised as being “adjusted for 5 positions,” that’s what it means. Older pocket watches will also say “adjusted for temperature,” but that’s not required with modern materials these days.
Sellita SW330-1 on its tech guide
Each movement will have its own requirements for positional adjustments and “delta,” which is the total difference between rates. That is, a watch that gains +30 seconds per day in dial up and loses -30 seconds per day in stem down will average to have a perfect +/-0 s/d rate, but will have a delta of 60 seconds, and keep erratic time in use.

The Sellita SW300 in our Olmsted is required to be adjusted in 4 positions with maximum/minimum rates of +/- 5 s/d and a total delta of 20 seconds, but we typically try to do better than that, with an average rate of +0 to +10 s/d. As a watchmaker, I like to adjust to 5 positions to ensure proper timekeeping in use, as well, so any watch that comes through for service will leave my bench adjusted to that standard.

Now let’s dig into why a positional errors occur, and how to fix them.

The balance wheel doesn’t spin, it oscillates back and forth. Typically, a balance wheel turns about 270° in either direction, so irregularities in the wheel can have an effect on its rotation and effective mass.

If the wheel turned fully, a heavy point would spend equal amounts of time at all points around the circumference of the wheel. But since the wheel doesn’t fully turn, some part of the wheel is “up” and the opposite is “down” for most of the rotation, so a heavy spot can start to have a pendulum effect.

Small irregularities in the wheel are always present. Try as we might, no component is perfect, and heavy spots can even occur because of tiny variances in the density of the metal used to form the wheel. That’s why, if you flip a balance wheel over, you’ll see some tiny slots or holes.
Poising mark on the underside of a watch's balance wheel
These are called “poising marks,” and these days are typically made by a machine during manufacturing. The balance wheels are fully assembled and then tested on a very sensitive device to find the heavy spots. Modern machines are excellent at this, and can usually equalize the weight in a single slice, while hand-poised wheels might take a few tries.
Manually poising a balance wheel with a handheld cutter
Poising a balance by hand requires immense care, and is done with an incredibly small carbide-tipped drill. The tiny shavings seem almost too infinitesimally tiny to measure, but they are enough to make a difference.

Static poising like this makes a huge difference, but isn’t the end of the story.

The hairspring is also affected by gravity, and we can’t go around drilling holes into it, so instead a watchmaker simply has to make sure that it’s as perfectly-formed as possible.
Flat & centered hairspring in a vintage pocket watch
Hairsprings must be perfectly flat and round to perform properly. All of the coils should have an equal gap, and there should be no “wobble” while it expands and contracts. Any problems have to be very carefully adjusted with tweezers—on coils of wire that are just microns thick. Frankly, hairspring adjustment is one of the finest and most challenging exercises for a watchmaker, but it can make all the difference.
Hairspring through regulating pins in a vintage pocket watch
As previously mentioned in the last article, hairsprings must also be adjusted to fit perfectly through the center of the regulating pins so that they don’t accidentally spend too much time touching one pin or the other. The total width between the pins will make a watch run faster or slower as well, and can be used to equalize rates between the dial and stem positions.
Free-sprung hairspring in a fine Swiss watch movement
Free-sprung balances actually have more challenging adjustments here—they rely on perfectly poised balances and ideal hairspring shapes, since there are no pins to help equalize any pre-existing errors.

This is all very complex, and it’s why regulation is one of the most challenging and critical parts of a service. Assembling a movement, after all, is delicate but straightforward. Regulation requires an entirely different state of mind and activity.
This is the third part in a three part series about regulation.