Jens Olsen’s World Clock

Jens Olsen’s World Clock is claimed to be the most precise mechanical clock in the world only outdone by atomic clocks.

But who was Jens Olsen and what was the driving force behind this modest Dane’s ambition and persistence that, despite great adversity in life, stubbornly worked all his life on his vision of a very special astronomical clock.

How I Got to Know About Jens Olsen’s World Clock

When I went to primary school a long time ago we got to know Jens Olsen’s World Clock in a lesson.

It was one of the more exciting lessons because what we heard was a story of a masterpiece created by a genius, even a Danish genius! I’m Danish so it made it no less interesting to me.

I do not remember which teacher or school subject we had, but I very clearly remember the story of this amazing clock and how much an impression it made on me.

I have explored the story again to fill the gaps in my memory and to learn more about who the man behind this incredible clock was.

Childhood and Youth

Jens Olsen was born in Ribe, Denmark on July 27, 1872 in a small home with a large family.

The family was poor, but the home was cheerful, and Jens’ peers were happy to make a visit where they would read aloud, sing and play music.

It was during one of the storytellings that Jens was inspired to become a watchmaker.

One of the stories was about a clock that had broken, but no one could repair.

Jens thought this could not be right and therefore he wanted to become a watchmaker when he grew up, so he could repair the watch.

In school, Jens had special abilities for mathematics and physics, and after finishing school, he was apprenticed to a locksmith.

Jens Olsen became a journeyman and worked as a mechanic for a while, and in his spare time, he read books on astronomy and all that was related to clocks.

Journeyman on a Journey

In 1897 Jens Olsen went on a 5-year foreign trip where he among other things studied the famous third clock in Strasbourg Cathedral, France (Cathédrale Notre-Dame de Strasbourg), constructed by Jean-Baptiste Schwilgué in 1842.

He tells from here that the times the clock was available for visit were no longer enough for him. Therefore, he hid in a corner of the cathedral and later he could study the details hour by hour!

His goal was by no means to copy this clock, but rather to learn and seek inspiration.

Jens also reached Switzerland where he worked exclusively with watchmaking.

Later he worked a year and a half in Paris, among other things, during the World Exhibition in 1900.

The journey ended in London.

Outlining the Project

Already during the journeyman years, Olsen had laid the first plans for his actual work of life, a modern astronomical clock that was supposed to surpass all the former in accuracy and the number of functions.

The first sketches were completed in 1922, after which Olsen built a preliminary model of the clock’s very ingenious calendar work.

Later, a detailed presentation of the whole clock followed.

Danish astronomer and Professor Elis Strömgren supported Jens Olsen’s ambitious clock project all the way and helped to ensure that all calculations were correct.

However, it took another twenty years to acquire the funds necessary to build the clock.

Did You Know That Jens Olsen’s World Clock:

  • is the most precise mechanical clock in the world and only outdone by atomic clocks.
  • has been gilded with four kilos of gold.
  • consists of 14,448 parts.
  • calculates the dates of the religious holidays and full moon of a coming year. It makes the calculations within six minutes at midnight on New Year’s Eve.
  • has the slowest turning gear in the world (25.753 years!).
  • was started by King Frederik IX Thursday 15 December 1955 at exactly 3 pm.
  • is winded up once a week.
  • has rhodium coating on all metal faces in the clock. Rhodium is one of the rarest and most valuable precious metals in the world. It is resistant to corrosion – it even remains insoluble in acid.
  • mainly consists of brass parts that derived from melted down kitchen utensils from Danish households of the 1940’s.

The Funds

In 1934, the watchmaker’s organization set up a committee with mayor Ernst Kaper as chairman to raise funds for the execution.

After Kaper’s death, the work stopped until 1938, when the watchmaker’s organization and H. C. Ørsted Foundation granted money for the preparation of work drawings that were completed in 1943.

A donation of DKK 100,000 from the Danish Employers’ Association supplemented with funds from a national fundraising then made it possible to start the work in a workshop that the Danish Technological Institute made available to Jens Olsen and his son Martin Olsen as an assistant.

The son was shot by the Germans during the public strike in 1944, and after Jens Olsen’s death the following autumn it was handed over to watchmaker Otto Mortensen to lead the clock’s completion and set-up at Copenhagen Town Hall where on 15 December 1955 King Frederik IX and Jens Olsen’s youngest grandchild started the clock in union.

Jens Olsen´s World Clock in Short

The clock’s central part is a pendulum clock (with Denison escapement) showing star time and middle European time.

From here, ten other works are managed, each of which shows significant astronomical and timing phenomena.

The clock is distinguished by all the earlier such clocks, partly by the ingenious execution of the solar and moon mechanism, and partly by the calendar work that each New Year’s night automatically calculates all the chronological elements of the coming year.

In addition, all clock parts are visible and very beautifully crafted both artfully and artistically.

Jens Olsen’s World Clock in Detail

Left Section

  • The top dial shows the time equation, local time in Copenhagen and actual solar time.
  • The time equation means the time difference between local time and actual solar time. Local actual time is the time usually used. Actual solar time expresses the earth’s position proportional to the sun. When the hands of actual solar time show 12, the sun is in meridian.
  • The dial to the left shows the time at any location on earth.
  • The dial to the right shows the time of sunrise and sunset both according to local time and actual solar time. The dial is equipped with black and white arch-shaped pieces to indicate the lengths of day and night.
  • The Gregorian calendar shows the year, the day of the week, date and month. This perpetual movement sets itself once every 24 hours at midnight.

Middle Section

  • The top dial, divided in 12 hours, shows local mean time – Central European time, the daily time 15° east of Greenwich in hours, minutes and seconds.
  • The perpetual calendar consists of 5 dials, indicating: The Sunday letter, the epact, the sun circle, the indiction and the moon circle.
  • Furthermore, there is a calendar showing the 12 months of the year, the days and dates of the week, every moon phase as well as the calculated Easter Sunday – all other holidays according to Easter Sunday.
  • The works of the perpetual calendar are automatically set in motion every New Years Eve at midnight, to calculate the calendar for the following year.
  • It runs for the next 2500 years.

Right Section

  • The top dial shows the present star map over Denmark and the slow precession of the motion of the earth’s axis over 25.753 years!
  • The left dial shows the geocentrical orbit with the Earth as its centre. Here you can obtain knowledge of the sun’s and moon’s eclipses, the distance between the Earth and the Moon – the apse line and the knot line.
  • The right dial shows our solar system with the planets Mercury, Venus, the Earth, Mars, Jupiter, Saturn, Uranus and Neptune around the Sun.
  • The bottom dial shows the year and number of days according to the Julian time period which is 7.980 years.
  • Astronomers use the Julian Time period to register astronomical phenomena.

The Personality Jens Olsen

It has been a great pleasure for me putting this article together about Jens Olsen and his incredible work of life, especially because Olsen was not just a skilled man, but also a well-liked person with the heart in the right place.

Jens Olsen was modest, but happy and friendly with a strong family feeling.

His humor made him popular among craftsmen in Copenhagen, just as his great technical and theoretical knowledge created respect for him in scientific circles where he already established his name in 1906 as one of the founders of the Astronomical Society.

So next time you come to Copenhagen, make sure to visit the City Hall and experience Jens Olsen’s World Clock up close.


  1. Photos by Dr. Gerhard Huber.
  2. “Jens Olsen’s World Clock in Detail”. Technical description from ateliera.dk.

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Claus is a laboratory technician, autodidact guitarist, songwriter, music publisher, co-founder of App Division ApS, dad of fraternal twin boys, Sci-Fi lover, incarnated Mike Oldfield fan, pro world peace and an incorrigible coffee addict.


  1. Oh how I love clocks and time pieces and this was such a great story of the great Jens Olsen.  How interesting that he made the most precise mechanical clock in the world (except, as you note, for the atomic clocks).  He lived so long ago, and to see what was possible even back then, and the precision he was able to use to create his clock.  

    Such a cool story about an awesome man.  Thanks for researching and sharing that!  

  2. What a fascinating story about Jens Olsens world clock! I enjoyed reading about Jens and his passion and his travels . He was an extremely hard working and dedicated man. Sounds like they translated into a real masterpiece of a clock. I’d like to see it one day. It sounds amazing!

    • Hi Emily, I’m glad you enjoyed my article. Besides the clock itself, there is an exhibition made in honor of Jens Olsen, so the next time you come to Copenhagen, you might want to visit the Town Hall and experience it all up close.

  3. This is an amazing clock with an incredible history. I can see why you loved learning about it in primary school! Clocks are really quite symbolic in our society, and although practical objects, they can be created so beautifully. I’m not sure what the cost to build it back then would translate to nowadays, but I’m sure it’s not cheap. The funds given show just how meaningful clocks can be for a society.

    • The fact that so much money was allocated to this project says something about how much people believed in the vision of Jens Olsen back then, doesn’t it. Thanks, Holly.

  4. Hi Claus, thanks for your informative review on Olsen’s World clock. I must say that Jens Olsen had an interesting childhood experience. Some stories really serve as motivational factor. I love the fact that Olsen was inspired to become a watchmaker after listening to a story where nobody could fix the broken clock. Jens Olsen was indeed a skilled man. I will definitely visit the City Hall one day. Thanks once again for your review.

    • Hi Gracen. I agree with you, stories of strong people’s determination and willingness to work purposefully are always inspiring.

  5. I have never heard about Jens Olsen nor about the world clock he made. This is a great writeup describing what inspired him, his life and journey and his inventions. Looking at what he created one would have wished that analog clock should stay relevant, but at the present age the digital clock is fast replacing the analog one. 

    • Hi Ayodeji, thanks for your comment. Jens Olsen was from a time before the digital age, so of course you are right. The beauty is that one can always learn from people’s challenges and how they overcame them, regardless of when they lived.

  6. Thank you for sharing this great information about jens Olsen’s world clock.

    This is the first time I hear about this jens Olsen’s clock and it was very interesting read about the history behind this clock, hopefully soon I can travel back to Europe and visit this jens Olsen’s world clock in Denmark,

    • Hi GVporras, I’m happy to learn that my post is reaching people who are unfamiliar with Jens Olsen’s World Clock. I hope you will be able to experience the exhibition one day.

  7. Very interesting topic and definitely kept me reading throughout the entire article. I love watches and clocks which is why I decided to take a look at this and ended up with a great history lesson. I have two other co-workers that collect watches and will be emailing this URL to them. Something unexpected but great lesson on clocks.

    • Hi Jason, thank you, I appreciate that. I think there are many people in the world who have never heard of Jens Olsen’s World Clock, so I’m only happy to help spread this amazing story.

  8. Different sources claim that the Jens Olsen clock is accurate to 1 second every 600 years, 750 years or 800 years. You also might care to look for Otto Mortensen’s 1957 book “Jens Olsen’s Clock”, which goes into great detail about the workings of the clock, and may give a more definitive answer about the clock’s accuracy. In 1991 various astronomical readings did not match an (astronomical) almanac. Between 1995-1997 a restoration of the clock was required that made long term improvements. You also might like Rasmus Sørnes’ ‘Clock No. 4’, the Rostock astronomical clock, the Besançon astronomical clock and Konstantin Chaykin’s ‘Moscow Comptus Easter Clock’.

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