What's the rate of a watch

Watch Talk: What’s the Rate of a Watch?

When it comes to watches, the rate is a very important if not the most important statistic. A watch might be very rare or beautiful but if it doesn’t keep accurate time, it’s basically useless.

What exactly is the rate of a watch? It’s how fast or slow a watch runs in seconds per day.

It’s inversely proportional to the amplitude. That means that a decline in amplitude will cause the rate to increase. If the amplitude is low, a balance wheel doesn’t have to “travel” that far so it takes less time to complete a beat.

That’s why so many older watches on eBay and flea markets run too fast. Dirt and hardened lubrication caused the amplitude to drop and the rate to increase.

A sticky or magnetized hairspring has the same effect. A magnetized hairspring will cause the watch to run much too fast and it’s one of the most common reasons that a watch doesn’t keep good time.

Finally, the position of the watch also has some influence.

In the horizontal positions (dial up and dial down) most of the downward pressure of the balance pinion is on the capstone, lubricated with some Moebius 9010. The friction is minimal and doesn’t affect time-keeping.

In the vertical positions, the friction is much greater because of the larger surface contact of the balance staff with the jewel hole walls. A change from a horizontal position to a vertical position causes a swing in the amplitude which in turn causes a fluctuation in the rate.

That’s why many movements are adjusted to 3 or 5 positions. It means that the watch is adjusted for positional error to make sure that the watch runs accurately in the most important positions.

What’s acceptable?

You’re probably looking for a clear and definitive answer but it depends.

It depends on the grade and the quality of the movement and the condition of the movement is also very important.

The COSC states that the average daily rate of a watch has to be within -4 and +6 seconds a day. However, many older movements and movements with a lot of wear won’t even come close to these readings. All you can do is try to get as close to 0 as possible.

I mainly deal with vintage watches and I always aim for a rate between 0 and +10 sec a day.

What is the rate of a watch
This is a Zodiac with an STP 1-11 movement. It has a decent rate of +5 sec a day. It also has a powerful amplitude of 308 degrees and a beat error of 0.1 ms

How do you regulate it?

With regard to the rate, it’s important to remember one rule. A shorter hairspring means faster and a longer hairspring means slower.

The easiest way to regulate the rate of a watch is with the regulator. The regulator has two pins and the first winding of the hairspring runs through them.

If you move the regulator towards the “slow” side, the index pins will move towards the stud. This will increase the effective length of the hairspring and the watch will run slower. If you move the regulator towards the “fast side”, the effective length of the hairspring will decrease and the watch will run faster.

What's the rate of a watch
This is a view of a balance from below. You can see the first winding of the hairspring between the index pins

Servicing the movement and possibly replacing the mainspring will also influence the rate because it’ll increase the amplitude. Replacing worn or damaged parts and correcting the side-shake and end-shake (replacing worn bearing jewels and checking the depth) has the same effect.

Magnetism causes windings of the hairspring to cling together, shortening the length of the hairspring. Demagnetizing the movement will lengthen the effective length of the hairspring and decrease the rate (longer means slower).

As you can see, the rate is a simple concept but it can be influenced by all sorts of things because everything is interconnected. It’s important to carefully study the movement to understand what you can do to adjust it.

Have you ever adjusted the rate of your watch? Do you have some tips on how to do so? Let me know in the comments below.

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