Your watch is wrong. No, really, it’s wrong.

June 21 marked the summer solstice and the “longest” day of the year. Chances are, you recall Earth Science class in middle school, or Copernicus or Galileo—and you know that it represents our hemisphere’s tilt to the sun. But did you know that it also means a day is not uniformly 24 hours long?

The most accurate “time keeping” device ever created is a sun dial. Trouble is, it does not work at night. But what do the earth’s orbit and an ancient sun dial have to do with the time shown on your watch? It goes like this…

The Earth’s elliptical pattern as it rotates around the sun means that at some points it is closer and at others, farther away (i.e. December 21—the “shortest” day of the year). This means that each day cannot be exactly 24 hours. That only happens on four days in a year: April 15, June 14, September 1, and December 24. At various times along this journey around the sun, the difference between “solar time” and your watch can be from plus 14 minutes and 22 seconds to minus 16 minutes and 23 seconds.

The Equation of Time is one of the Eight Mater Watch Complications that actually tracks the difference. Press the button and the extra watch hand (usually indicated with a sun on the top) moves to the solar time position on your watch, showing you the difference.

Keep in mind that this technology was created during the heyday of watchmaking (1700’s to 1800’s), in the Vallee du Joux of the Swiss Jura Mountains—equivalent to today’s Silicon Valley. No amount of 20th or 21st century technology can make this function more accurate. It’s incredible when you think that men with nothing more than a crude telescope, a quill, and some parchment could conceive, understand, and then create a machine to track Earth’s orbit around the sun and display it in a timepiece.

We created what is called “commercial time” as a way of regulating travel, trains, and daily life. Your watch shows commercial time as all have done for centuries. And though A Blog To Watch named the Equation of Time one of the “top 5 useless complications,” buyers, collectors, and manufacturers still covet this function as a window into a different time. Quite literally. In fact, one could argue that none of the master watch complications “improve daily life.” So why do they endure? Perhaps it is our fascination with these tiny mechanical throw-backs to a low-tech era.

It is rare to find the Equation of Time as a singular complication—most often it is one of a few in an ultra-complicated timepiece. Most the top houses manufacture an Equation of Time: Patek Philippe, Breguet, Balncpain, Vaheron Constantin, Corum, Ulysse Nardin, and many others. Eleven James enables you to select from a range of Equation of Time options in the Virtuoso collection to see which best suits you. Regardless of your choice, the story behind this complication is sure to fascinate your friends and score you points in the trivia contest!

– JOSEPH PANETTA

Pictured: Sundial by Alexander Stirling Calder, 1903

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