How Do Watches Know The Date


Many watches nowadays not only display the time, but also the month and even the date. But how does a watch know the date is?

A watch has a date reel of 31 days that runs from 1 to 31. When you set the correct date, every 24 hours, the reel will show the next number, the next date. This means you need to manually correct the date during months with fewer than 31 days.

Manually correcting the date is a minor inconvenience and shouldn’t deter you from a watch. However, there are actually some watches that have a more complex system in place that requires less manual adjusting.

How Does A Watch Keep Track Of The Date

For some people, a watch can seem like a miraculous little accessory. It knows the time, displays it perfectly, and it can even show you the date and month. And all of that in such a tiny little piece.

In general, most watches are connected to the central timepiece and have a date reel of 31 days. This date reel is connected to the central timepiece and will move with every 24 hours that pass. As you can imagine, a watch does not know when a month has only 30 days, so every now and then, you’ll need to manually correct the date.

Most watches will feature this type of ‘Calendar Reel’, as it’s the easiest and cheapest way to go about it. You can, however, find some high-end luxury watches that are able to keep track of all the dates without you having to manually adjust them. More on that later, though.

As mentioned before, a watch with a normal calendar reel will need to be manually adjusted from time to time. When we’re counting from January 1, then you’ll have to manually adjust the date a total of 5 times:

  • February only has 28 days (or 29 during a leap year)
  • April has only 30 days
  • June has only 30 days
  • September has only 30 days
  • November has only 30 days

Only having to adjust the date a total of 5 times per year is a minor inconvenience and with most watches, it’s an extremely easy process.

It should also go without saying that a smartwatch will need no adjusting. Technology has come very far, and displaying the right time on a piece of electronics is a simple feat.

How Do You Manually Adjust The Date

Manually adjusting the date on your watch should be a rather easy task. Your best move is to look at your watch manual. Here, it will probably be described how to adjust the time and date. Usually, if you change the time, your date changes with it. So, if you can’t adjust the date manually, you can always move the time 24 hours forward.

However, if you don’t have a manual, here is how you can change the date on your watch:

  1. Pull out the crown a bit. The crown is the small ‘knob’ on the side of your watch. You can carefully pull this out a bit.
  2. Start turning the crown clockwise. Turning it clockwise will set forward the time and once you’ve passed the 00:00, the next date should display.
  3. Always avoid turning the crown counterclockwise. Turning the crown counter-clockwise can damage the mechanism in the watch, which you would want to avoid at all costs.

The Mechanics Of A Watch Displaying The Time

The mechanism inside a watch is, of course, extremely complicated, but most watches follow a similar sort of structure. For the watch to show the correct time, there’s a central piece that perfectly follows every second, ensuring it displays the time correctly.

If you have an analog watch, which can either be mechanical or quartz-based, you’ll have a motion work that ensures the correct time is displayed. Connected to the motion works is a ‘reduction gear train’, which moves with it. 

Every 24 hours, your calendar reel will be moved completely, showing the next number on the reel. This will also work if you adjust the time to any time of the day, as the reel will just move with your adjusted time. It’s actually a very simple process, but seeing that all of this takes place in such a small little object is mind-blowing!

Annual And Perpetual Calendars

Besides the standard ‘Calendar Reel’ we discussed, there are two more options, usually found in higher-end watches. One of them is called the Annual Calendar and the other is called the Perpetual Calendar.

These are two more sophisticated options that require much less manual adjusting. This, of course, comes with a higher price, and even then, not every luxury, high-end watch will have this feature.

First, let’s discuss the annual calendar. When your watch has an annual calendar, your watch will be able to keep track of both 31 and 30 day months. This simply means you only have to manually adjust it one time per year. Since your watch will be able to keep track of both 30 and 31 days, you’ll only need to manually adjust it on March 1st, since February only has 28 days.

A watch with an annual calendar will display the date, day, and month with minimal need for adjusting. It can track both 30 and 31 day months, leaving you with only one needed adjustment at the start of March.

 This is of course a great feature and definitely takes away some of the hassle. Even though manually adjusting it 5 times per year is a minor inconvenience, only needing to adjust it once a year is much better.

On the other hand, you have a perpetual calendar. This is an even more advanced version that not only knows every month but also every year. What this means; a watch with a perpetual calendar won’t need to be adjusted until 2100. It will automatically adjust for every month, including February and it will even know when it’s a leap year, adjusting correctly for that as well!

A watch with a perpetual calendar will know all the dates, months, and years up till 2100. It will correctly display every month, including February, and it will even adjust for a leap year. This leaves you with a total of zero manual adjustments until 2100.

A perpetual calendar is, of course, the best sort of watch calendar you can get. It leaves you with zero manual adjustments until 2100, taking away even the slightest of inconveniences.

What Watches Have An Annual Calendar

As mentioned before, watches with an annual or perpetual calendar will probably come at a much higher cost.

The Patek Philippe Annual Calendar line is a watch line with watches that have an annual calendar. The name already suggests its annual calendar and we all know that a Patek Philippe costs a good buck. 

Many of the Patek Philippe Annual Calendar watches offer a sleek and timeless design that’s a little more minimalistic and straight forward. In other words, they look amazing and go great with just about any outfit.

The added bonus, of course, is that you only need to adjust the date once a year. However, this does come at a price. With any of the watches in this collection, you can look at prices ranging from $15.000 to $50.000.

What Watches Have A Perpetual Calendar

An example of a watch with a perpetual calendar is the Jaeger LeCoultre Master Eight Days Perpetual. This is a gorgeous watch sporting a 42mm diameter and rose gold case. 

Once again, this is a more expensive watch, coming in at around $20.000 to $30.000, but you definitely get something amazing. It looks fantastic, shows the day, month, and the time of the day.

On top of all the features, you won’t need to manually adjust the date throughout the year. This is a perpetual watch, so you’ll have to wait around 80 years for your first manual adjustment!

Closing Words

Watches are amazing little accessories. They look great, are functional, and there’s a lot of craftsmanship behind them.

A watch displays the date with the help of a calendar reel. This calendar reel is connected to the central timepiece and moves the time. After every 24 hours, the reel will have turned enough to show the next date.

Your standard calendar reel will have 31 days, which means you need to manually adjust the date 5 times per year. However, there are also options that require much less adjusting. A watch with an annual calendar will need to adjust only 1 time per year, at the end of February. There’s also an option that only needs adjusting once per 100 years. This option is called the perpetual calendar.

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