Watch Works

Watch Works: How A Mechanical Watch Works


Today we are going to look at a complex mechanical watch movement and attempt to explain it simply. We focus on a few key components of the movement which are often mentioned. So the next time you read about a watch and its movement, you’ll know what they mean. The movement under the loupe is the Perpetual Calendar Calibre HMC 341 from H. Moser & Cie.


The mainspring is where the watch gets all its power from. The main spring is housed in what is called the barrel. In the background of the below picture you get a glimpse of parts of the gear train which is in connection with both the mainspring & escapement (more on the latter below). The gear train constitutes more or less of the wheels & bits between the mainspring and the escapement module which make sure that the force of the mainspring is transferred to the balance wheel and the hands turn to tell time:

Assembly of the barrel

Pictured above is a single barrel being placed on the mainplate, the foundation of the movement. If more power is required you can have more than one barrel. In the case of the HMC341 you have a double barrel. And this leads to a whopping 7 day power reserve:


How you get the mainspring wound, and therefore powered up, is in this case by manually winding it at the crown. By rotating the crown, it’ll set in motion the crown wheel which will spin the ratchet wheel which tends to sit on top of the mainspring and as such will help coil it. To Avoid that the mainspring instantly uncoils itself, there’s a click which makes sure it can not unwind itself. It avoids that the crown wheel & therefore the linked up ratchet wheel & barrel can turn backwards under the mainspring’s tension:

Power up

When the click is pulled back, e.g. during servicing, the mainspring will unwind itself and the watch will remain without power.

Gotta keep it moving

There are a lot of moving parts in a watch movement, and where there is movement there is friction. In order to reduce friction you will find jewel bearings in a movement. These are rubies in this particular case and they are cradled in ‘chatons‘:

A gold chaton about to be set

With the chaton now set in place, a close-up follows of a ruby which is about to be nested in the chaton. The metal structure is the bridge, but more on that below:

Up-close and personal with Ruby

In the little hole of this ruby donut, a spindle will spin away and experience the least amount of friction possible:

Nice and comfy

Stay put

As briefly mentioned, the metal structure pictured above is called a bridge. A bridge is used to help secure parts to the mainplate. One watch movement can have multiple bridges:

Barrel bridge

Bridges & screws go hand in hand. Hereunder a close-up of the different types of screws you’ll find holding the calibre together:


We need a heartbeat

Once the power source & gear train is all set and secured, the “only” thing left is adding the escapement module to transfer all that power in actual accurate time. What the escapement does is translate that raw & unregulated power from the main-spring to that familiar tick-tock, in this case at a rate of 18,000 beats per hour.

escapement module
Moser’s in-house interchangeable escapement module

The escapement wheel & pallet fork transfer the energy from the mainspring to the balance wheel at exact intervals. The pallet fork interacts with the balance wheel and the escapement wheel, this exact interaction is what creates that familiar ‘tick tock’ sound. The escapement wheel is the most Southern wheel in the below picture, it is the part of the escapement that touches the Gear train. The balance wheel is the wheel that rocks back and forth and cuddles the ever important hairspring, together they are the timekeeping element . Each swing of the balance wheel takes precisely the same amount of time. In a way, it acts much in the same way as the pendulum on old clocks which swing left & right. Overall, the escapement module is where art & science meet and consequently it gets really complicated and it consists of 59 parts in this case:

Moser’s interchangeable escapement module

Worth mentioning at this point is the unique characteristic & approach that H. Moser & Cie has with respect to the escapement module. They call it their ‘interchangeable escapement module’. What they have done here is take into consideration how to efficiently make & best service a watch. As per Moser, their interchangeable escapement has been “developed to simplify the adjustment, cleaning and servicing of the watch. It enables the watchmaker to remove the existing escapement module, clean and oil the rest of the movement before installing a new pre-adjusted module.” This escapement module is designed to be easily installed & replaced during service when needed. Very clever indeed.

Et voila!

And finally when all is said and done, when the calibre is fully assembled, you’ll have this glorious movement staring back at you:

Calibre HMC341


Photography note: Courtesy to @moserwatches for sharing the wonderful macro shots with the rest of us. Please respect their copyright. Sincere thanks to Olivier as well for making this happen, make sure to check him out on instagram here.

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Jill Troughton

Very well explained about Mechanical Watches. I really like your blog and its images which you uploaded. Thanks for this informative blog.

Jan de Griff

Great to hear, thanks! It helps to have the wonderful Moser movement as model 😉

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