An automatic watch contains a purely mechanical movement that is self winding, thus it is automatic. There are no batteries inside of the watch, and it can keep going for years without any winding whatsoever. There are gears inside of the watch that turn the hands and power the complications. These gears are turned by a spring called the mainspring.
The mainspring is constantly winding down driving the gears so it needs to be rewound. The way the mainspring gets rewound is from an oscillating weight that swings on a pivot. The weight moves around from the person wearing the watch. As you raise your arm to drink a beer or eat a taco the weight moves around inside of the watch and winds the main spring. If you stop drinking beer and eating tacos you stop winding the mainspring, so don’t stop.
That is the simple explanation of an automatic watch. So if you clicked on the link to this page and you were after the simple explanation, you got it. For a more detailed version keep reading.
History
If you can imagine, back in the 1700’s you had to wind your watch to keep it running. Now there is a debate of when and by whom the first wristwatch was created, one thing is certain, most watches around that time frame were pocket watches.
The automatic pocket watch was invented in Switzerland by Abraham-Louis Perrelet in 1770. Now this was designed to be wound by walking around. The thought at the time was you could walk for 15 minutes and that would wind the watch enough to run for a few days. It really worked like a pedometer, and some of today’s pedometers work on the same type of mechanism.
John Harwood was the watchmaker who put the automatic movement into a wristwatch and the version of the automatic watch we wear today was born. He actually was the first person to mass manufacture the automatic wristwatch. The reserve on this watch was about eight hours.
In the 1930’s Rolex revolutionized the mechanism so it wound from any direction it was moved. Harwood’s design only would in one direction. This new design was much more efficient and captured more energy in the mainspring, giving it a reserve time of more than 30 hours.
Today’s modern automatics have reserves that are 40 to 50 hours. Although it is the same basic concept invented in the 1770’s, the engineering and components have been refined to modern works of art. Modern automatics employ engineering making them shockproof and anti-magnetic.
Operation
As mentioned above, every mechanical watch has a mainspring that drives the hands and complications. This is really the heart of any automatic watch. Before the automatic was invented we had to wind the mainspring with the crown, the little knob on the side of the watch. The automatic watch has a weight or rotor that is typically shaped like a half of a moon. The weight sits on a pivot, which is at the center of the movement. The movement of the weight turns the pivot, the movement of the pivot turns a series of gears and reducers that it attaches to and this is what winds the main spring.
The main spring stores the power and over time unwinds itself to power the hands.
The easiest way to tell if a watch is an automatic is to look at the second hand. The second hand will sweep or have very little ticks per second as opposed to a quartz movement that has one tick per second.
Power Reserve
The mainspring has a finite amount of energy it can store. Clearly it is not limitless. The amount of energy it stores is called the power reserve, or just reserve. Depending watchmaker it may be longer or shorter, but most of them have a reserve of around one or two days. I think the longest power reserve for an automatic watch is seven days, but I’m sure that one is pretty expensive.
Some dive watches have indicators letting us know how much reserve is left. It’s a neat feature, but I think it kind of clutters up the beauty of the watch. I find if you are moving around a little bit during the day an automatic watch does just fine.
Complications
You may have seen watches with different things on the dial such as a date feature. This is called a complication. Anything additional to the hour, minute and second hand are complications or additional features the watchmaker built into the watch.
A list of additional complications are day, date, chronograph, moon phase, dual time zones, triple calendar, power reserve, and many more. I think the common complications found on dive watches are mostly the date and day.
Hand Winding
Many automatic watches have a hand winding feature, so if the watch stops because you didn’t wear it for a week it allows you to wind the spring to start working. It is recommended to wind it 20 or 30 turns to wind the mainspring. Not all automatics have this feature, and in that case you just need to start wearing the watch for the weight to wind the mainspring.
To wind the spring, you do this by pulling out the crown to a certain position and generally turn it clockwise. Your owners manual will tell you which position the crown needs to be in for hand winding.
There is no need to worry about over winding the watch, there is a mechanism inside of the watch that lets the mainspring slip as to avoid damage by over winding.
Hacking
Many automatics have a feature called hacking, this is where you pull the crown out and the second hand stops. This allows you to synchronize watches, or set it to the exact time. Once you push the crown in the second hand starts moving again.
Accuracy
Are automatic watches accurate? Yes, they are very accurate. Most automatic watches lose or gain a few seconds a day. However, there are very high end automatic movements that have even better accuracy.
A lower end automatic watch may gain or lose 20 seconds a day whereas a high end chronometer will be as accurate to within -4 to +6 seconds per day.
There are different standards, COSC is one of the most popular Swiss standards, if you have a certified Chronometer you own an extremely accurate automatic watch. A certified chronometer is going to cost thousands of dollars. Most automatics are extremely accurate without being certified as a chronometer at a fraction of the cost.
Owning a purely mechanical watch that exhibits this type of accuracy is a marvel. However if you are after near perfect accuracy you probably should purchase a high end quartz movement.
The automatic watch movement is 150 years old. It is not a new technology, yet there is a simplicity about an automatic watch. There are more accurate movements, but they don’t have the character of the auto.
Servicing
Automatic watches do need servicing from time to time, usually every five years or so but it depends on the watchmaker. Like a truck engine, they have moving parts that have wear. They do require a little oil on the gears and other parts. So it’s best to find out what service interval your watch requires and have it serviced on that schedule, kind of like changing the oil in your truck.
This is more important for dive watches, because they have o-rings and gaskets that keep the water out, but as far as the movement goes, every five years or so seems standard. Consult the watch maker to be sure.
Something to note is that like cars, automatic watch movements have different prices when it comes to servicing. Some are every economical and some are very expensive to have serviced. This is something to consider and ask your local watchmaker before buying an auto. If it costs a lot to service the movement and parts are not readily available you may want to reconsider.
Jewels
Have you ever seen an advertisement claiming how many jewels a watch has? It seems like watchmakers are bragging with how many jewels they can cram into a watch, certainly making it more expensive in the process.
No that’s not it at all, the jewels inside the movement actually have a purpose. They function as anti-friction devices. All of the gears, springs, wheels and pivots are made of metal and create friction. Over time this friction wears on the metal parts. So what watchmakers do is put synthetic sapphire jewels inside the watch at key friction areas so the movement isn’t wearing itself out.
Sapphire is a very hard stone, nearly as hard as a diamond. So it wears out much slower than any type of metal they could use.
Each watchmaker puts a different amount of jewels inside of the movement based on how it is constructed. More jewels isn’t better, it just has however many it was designed to have. For example a Seiko Caliber 7s36 movement has 23 jewels, you cannot add a few here or there if you wanted to, it was designed to have 23 jewels. The Seiko Caliber NH36 movement is designed to have 24 jewels.
Final Thoughts
An automatic watch movement really is an engineering marvel. You don’t buy one to have the most accurate watch on your wrist. You buy one because something about it speaks to your soul. No battery, no winding, it just works.
If you’re interested in the differences and similarities between an automatic vs. solar watches click on this post.
Let me know if you think I missed anything in this post regarding the automatic movement. You can reach me on my contact page.