Before we delve into automatic watches and their characteristics, it’s very important to clarify that manual and automatic watches both belong to the same big family of mechanical watches.
Left: Automatic Watch Right: Quartz
As opposed to quartz watches which get their energy from batteries, mechanical watches receive their energy from the unwinding of a coiled flat spring called a mainspring.
Above: A Watch Mainspring Below: Illustration showing how it combines with a barrel
So how does it work? How does the watch wind up when I’m wearing it?
As mentioned above, the vast majority of automatic watches behave like manual watches and therefore, like a manual watch, one way to wind an automatic watch is via the crown.
There are of course some exceptions to the rule, like the SEIKO 7S26, that can only be wound up via its automatic mechanism.
However, due to the difference in the automatic winding system itself, you will never reach an “end point” when winding an automatic watch manually via the crown, like you would when winding a manual watch. Let’s try to explain the reason.
Every automatic winding system relies on the principle of inertia. Inside the mechanism is a freely oscillating weight (most of which rotate but there are some which can be translating) which is connected to the mainspring. Everytime you move with the watch on your wrist, this weight stabilises itself (like a wobbly man stabilises himself when pushed), and through a geared connection subsequently winds the mainspring up, little by little.
Now, usually after several hours (depending on the design), the watch will be fully wound up. The problem you might already foresee here is that if the mainspring had an “end point”, like the one you reach when you wind up a manual watch, the automatic system would reach it and eventually go beyond, most likely causing a component to finally break.
To avoid this problem, watch engineers have devised a special kind of mainspring that gently slides inside their container when they reach their highest tension. Hence, strictly speaking, winding an automatic watch does have an end, but it’s continuously sliding, so you can’t actually feel it.
Does it make my automatic watch any better than my manual watch?
Automatic systems are not only convenient for the user, but also due to how the watch mechanism behaves when its mainspring slowly unwinds, it’s also likely to help it give the best performances.
If you fully wind a manual watch after strapping it on in the morning, the mainspring will slowly unwind during the day, and even with the latest modern mainsprings, its physical properties will vary slightly. Consequently, the accuracy of the watch is more likely to vary during the day.
A watch being tested for accuracy
There’s a subtle difference in an automatic watch. If you fully wind an automatic watch in the morning and keep moving all day, the mainspring will keep a high tension, and therefore the watch will run in more consistent conditions. Therefore, the accuracy of the watch is less likely to vary during the day.
It’s really important here to remain critical: of course, a quality manual watch will beat a cheap automatic watch, anytime.
If it’s more convenient and likely to be more accurate, why do brands still make manual watches?
Manual watches are the most basic form of mechanical watches. It’s part of their appeal, and it’s a good enough reason for them to exist.
Some mechanical watches are extremely beautiful and the lack of rotor allows you to see the movement in its fully glory
On a more pragmatic point of view, they are simpler than their big sisters – the automatic watches, and therefore less likely to break down.
How long before my watch stops when I put it to rest?
Say you have been wearing your watch all day. If you have been active enough, it should be fully wound up. From there you should be able to answer the question. When put to rest, an automatic watch will behave exactly as a manual watch: it will work until the power reserve has been used up, say between 40 and 50 hours.
Your watch should be ready for Monday morning even if you aren’t
This actually works out quite conveniently in real life, because if you leave your automatic watch to rest after having worn it all day on a Saturday, it will still be keeping time when you take it back on Monday morning (you might not wear a watch on Sunday, or maybe a different one).
When I put my automatic watch back on, do I need to wind it up a bit manually or just give it a bit of a shake?
In the morning, when you reach over and put your automatic watch on your wrist in preparation for the new day, it has most likely been working for more than 10 hours, which corresponds roughly to 25% of is power reserve. It will have about 75% left before the energy runs out, and the automatic system will work during the day to catch up what was spent during the night- so it’s no big deal.
An automatic wristwatch gives it’s best performance when fully wound
Despite this, keep in mind that your automatic watch will give the best of its performances when it’s fully wound: if you leave it to rest for one complete day or more, you should manually wind it before you put it back on.
What is a Watch Winder?
Some watchwinders are quite beautiful
If you have only one mechanical watch with a simple complication, it’s rare that you ever leave the watch long enough alone, that it stops moving.
Due to the price of some watches, some watchwinders are designed to be similar to a safe
However, instances such as perpetual calendars, which display many complications and are tricky to set, or people having possession of more than one watch, mean watch winders are a much welcomed convenience. They are essentially boxes in which automatic watches are kept in motion when they are not in use. Since they are constantly moving inside the watch winder, they are always fully wound up and therefore always ready to go.