What Is an 8-Day Clock?

What Is an 8-Day Clock?

Updated: January 14, 2022

It may seem like clocks run forever, but they don't. Unless your clock uses electricity as its main power source, a mechanical or battery-powered clock will eventually stop working.

With battery-powered clocks, you never know when the charge will run out. But with a mechanical clock, there tends to be a very specific timeframe for how long the gears will run before it stops, and you need to re-wind it.

In this article, we'll answer the question "What is an 8-day clock?" and provide an overview of how 8-day and 31-day clocks work.

What is an Eight Day Clock?

An 8-day clock is a type of mechanical clock. More specifically, it's a mechanical movement clock that must be wound every eight days with a key for it to continue working.

Put plainly, they are called 8-day clocks because they last for eight days before the mechanism needs to be re-wound.

Similarly, you can find 14-day, 15-day, 31-day, and even 60-day clocks. The number simply represents the days the clock runs before it needs re-winding.

How Do 8 Day Movement Clocks Work?

Since an 8-day movement clock is a type of mechanical clock, it needs to be wound with a key for it to work.

When you wind a clock, you tighten the mainspring. Once the spring has been tightened, it naturally unwinds itself over time. This movement turns the gears and causes the clock's hands to move around the face.

Some eight-day clocks have a pendulum which helps keep the time accurately. When the pendulum swings, it ensures the gears maintain a consistent pace that moves with the seconds.

If your clock has a pendulum, always ensure it rests on a flat surface. Uneven surfaces can cause pendulum clocks to swing unbalanced and therefore tell the wrong time.

With proper maintenance and care, an 8-day movement clock can accurately tell the time for years. If your clock continuously falls behind or doesn't complete its full 8-day cycle, it may need a service or a deep clean to work properly again.

How Do You Set an 8 Day Clock?

Setting an 8-day movement clock is easy, but it requires patience. Winding the clock too quickly can cause the gears or inner mechanisms to snap.

To set an 8-day clock:

  • Turn the key slowly and smoothly - this can be clockwise or anticlockwise, depending on the type of 8-day clock you have
  • Stop turning when the spring feels tight

During winding, be careful not to let the key snap back each time you release it as this can damage the mechanism.

For the best results, try to keep a consistent schedule and wind your clock on the same day every week.

If the time has fallen slightly ahead or behind during the week, you may also need to adjust the time before or after winding.

What is a 31-Day Korean Clock?

Similar to an 8-day clock, a 31-day clock is a type of mechanical clock that lasts for 31 days before it needs re-winding.

Mechanical clocks that run for 31 days have been produced in many places around the world over the decades - including Japan, Germany, China, America, and Korea.

Tributes to vintage 31-day clocks cite that Korean mechanical clocks have different appearances and mechanisms compared with other designs developed around the world.

Some sources say that 31-day Korean clocks with vintage mechanisms also have above-average time-keeping abilities.


Owning a vintage, 8-day mechanical clock is a charming way to admire the development of mechanical movements and their accuracy in keeping time. Through proper care, servicing, and maintenance, you can enjoy a mechanical clock for generations.

If you're interested in learning more about how clocks work, check out the alarm journal for more information about time.

Author: Burak Özdemir

My name is Burak, and I used to have difficulties waking up in the morning due to unreliable alarm clocks. Over the past few years, I've dedicated part of my life to finding the best alarm clocks and sharing my knowledge with people through this blog. I'm also the creator of Online Alarm Clock.