A watch with a perpetual calendar, what is it?

What is a perpetual calendar, what is a watch with a perpetual calendar and how useful is it? Well, a perpetual calendar is meant to tell you what day and date it will be at any point in the future. And with that description, we are already halfway there! But there is more, much more. In this blog, we'll explain it to you.

Perpetual but not infinite?

Before we go any further: Eternal lasts a really, really, really long time. And a (mechanical) 'perpetual' calendar might be able to tell you what date it is in the far future, it is not eternal. So it is actually not perpetual at all simply because you can't go on displaying dates indefinitely with a calendar. Somewhere in the very distant future, your calendar will get out of sync because time is eternal and there will always be a deviation in time. Also, a calendar tool can not go on working for eternal. But it might just help you out for a long time to come, long enough to be a useful tool.

Citizen watch with Perpetual Calendar & moon phases

Even and odd months, leap years...
A perpetual calendar is pretty complex

Displaying 'perpetual' dates is quite a thing. After all, there is quite a difference in numbers of days per year and days per month. Leap years, months with 28, 29, 30 or 31 days, have to be taken into account. Week numbers also shift annually. For a mechanical instrument this is pretty complex.

Example:
If January 1, 2018 falls on a Tuesday, the January 1, 2019 will be on a Wednesday. But note: not in a leap year. A leap year has one extra day so a date will shift not 1 but 2 days. Try taking that into account with a mechanical calendar, it takes a lot of gears!

Perpetual Calendars in the Middle Ages

Already in the Middle Ages people made perpetual calendars. Not as a luxury, but because a perpetual calendar was a cheaper solution than an annual calendar. Those yearly calendars had to be made every year and that was an expensive production process before and just after the invention of printing.

A perpetual calendar was enough for a longer period of time. So much easier and cheaper in the long run.

Mechanical calendar

The invention of a mechanical calendar led to the creation of a useful mechanical instrument. An instrument that enabled people to figure out a particular date in the future. To do this you needed to know at least the year and month. A perpetual calendar is able to tell the correct date and day, taken in to account the leap years.

Also read: 'How to set the date on your watch in five steps?'

Some perpetual calendars are made even more complicated by adding the phases of the moon. Such a calendar soon becomes half a planetarium!

Citizen Promaster

Watch with perpetual calendar

It's quite a technical feat to build all this mechanical ingenuity into that a small tool like a watch. Making all that possible with cogs and wheels is quite clever. A watch with perpetual calendar is able to tell the correct date, taken into account even/uneven months and leap years. It is therefore you'll find that watches with a perpetual calendar are a bit more expensive then watches without a calendar. 

First watch with perpetual calendar

The first (pocket) watch with a perpetual calendar was invented by the British Thomas Mudge in 1762. You can see this special gold watch in the British Museum. This 'device' was far from being a wristwatch. It took two centuries before the first wristwatch with perpetual calendar was marketed by Patek Philippe. Thanks to modern technology like smartphones, computers and the internet, perpetual calendar watches have become a lot more common.

What is a 'PCAT' watch?

PCAT means: 'Perpetual Calender Atomic Timekeeping'. It is a combination of a perpetual calendar with atomic time keeping, watches that use the atomic clock to tell time. A lot of Citizen watches are equipped with an atomic clock-driven movement and a perpetual (perpetual) calendar. A watch with atomic time keeping is very accurate and some models are able to tell time with a deviation of only a few seconds in a Million years!

Perpetual calendar watches at WatchXL

If you are looking for a watch with a perpetual calendar we recommend you to take a look at our perpetual calendar watches. WatchXL has a number of watches with perpetual calendar. For example Citizen watches with Citizen E660 movement. This timepiece has very extensive features including a perpetual calendar.

Citizen Promaster with perpetual calendar

So a watch with a perpetual calendar is a really usefull tool. A time piece that will keep you up to date for a long time to come!  Find your perpetual calendar here.