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Rolex Bezels: How to use the Cosmograph Daytona Tachymeter Bezel

April 19, 2018

BY Paul Altieri


The Rolex Cosmograph Daytona technically made its first appearance in 1963 as the Rolex Cosmograph.  Equipped with a bezel engraved with a Tachymeter scale, the Cosmograph, or Le Mans, laid the foundation for what would later be known as the Daytona sports watch.  It wasn’t until after Rolex became the official sponsor of the Daytona Speedway that the Cosmograph appeared with both the name “Daytona” on the dial and the Tachymeter bezel. 

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The History of the Daytona Tachymeter Bezel

Since its release, the Daytona has seen many bezel variations, including stainless steel and plastic in early references and, more recently, aluminum, ceramic, and white gold.  The Tachymeter bezel’s primary function is to measure average speeds per hour while traveling, a feature that was initially developed by Rolex in a bid to become the official watch of NASA, hence its original name “Cosmograph”.  Instead, Rolex’s iconic chronograph found its home among the world of professional driving, with the Tachymeter bezel being used primarily to measure driving speeds. Early references allowed the wearer to measure driving speeds of up to 200 kilometers per hour, while later references were upgraded with a bezel that featured 400 graduations per hour.  

Through the years, Rolex has continued to improve upon the movement that powers the Daytona, evolving from such movements as the Zenith “El Primero” calibre 4030 movement to the Rolex calibre 4130 movement, which is made entirely in-house.  The movement plays a crucial part in the accuracy of the bezel calculations.

A black cerachrome daytona tachymeter bezel

A Black Cerachrom Daytona ref. 116500

Bezel Functions

As previously mentioned, the Tachymeter bezel is marketed as a tool for measuring driving speeds.  To use the bezel, you will also need to engage the side pushers to access the chronograph functions.  

  1. To begin, unscrew both the top and bottom pushers.  The top pusher will be used to start and stop the seconds hand.  The bottom pusher will be used to reset the display.
  2. Press the top pusher at the beginning of the distance that you wish to measure (such as a mile marker or the start of a lap around a racetrack); this will activate the chronograph’s seconds hand.  Once finished, press the top pusher again to stop.
  3. The average speed can now be read on the bezel. For Example, if you wish to calculate your driving speed over the course of 1 mile, press the top pusher to begin measuring.  Once you’ve reached one mile, press the bottom pusher to stop. The number indicated next to the chronograph seconds hand on the bezel is your average driving speed.
  4. Press the bottom pusher to reset.

You don’t have to be a NASCAR driver to take advantage of the Tachymeter bezel.  It can also be used to measure the approximate time it takes to do anything over the course of an hour at an average rate.





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