Last week we covered the Rolex Daytona, one of the watch industry’s leading chronographs.  When looking at a Daytona watch face one would expect to see “chronograph” on the dial, but in fact there is no such indication. What is found on the Daytona watch face (and on most other Rolexes for that matter) is  “Officially Certified Chronometer.”  Chronograph or Chronometer? Similar sounding but they signify two completely different aspects in the watch world.  One is a type of watch whereas the other is a timing certification related to accuracy.  Let’s uncover which one is which.


Last week’s Daytona review was one of a “Chronograph.”  A Chronograph, is a type of wristwatch with a build in stopwatch feature, hence the “-graph” suffix in its name.  Chronographs have one-to-two buttons on the side to for stopwatch activation and return to zero functions.  Chronographs also have two or three subdials, technically known as registers, embedded in the watch face to count seconds, elapsed minutes and hours.  Chronographs go back in history as being one of the harder watches to manufacture, work reliably, and keep waterproof because of the extra activation buttons and complexity associated with the stopwatch functions, and one of the reasons why the Daytona is considered such a thoroughbred in its class. Most chronographs have two or three subdials listing hours, minutes, and seconds. Spotting a chronograph is easy because the dials are typically busier with various registers, and have buttons on the case side.



A “Chronometer” on the other hand is a industry term for timing accuracy.  Most Swiss watches are not chronometers, but Rolex takes great pains to insure that their watches are in fact real Chronometers. For any wristwatch to gain Chronometer certification requires testing and accreditation from a certified independent standards laboratory normally associated with an observatory that measures the earth’s movement through space. Measuring the earth’s alignment with the sun, stars, and planets is the ultimate measurement of time prior to atomic clocks.  Before atomic clocks observatories such as the Kew, Greenwich, Glashutte, Besancon, Elgin and the U.S. Naval Observatory provided means for comparing and certifying watch accuracy. After the advent of atomic clocks, watch accuracy certification did not necessarily require an observatory to benchmark accurate time keeping, but many Chronometer certificates originate from these observatories.



The Swiss standard for accurate time keeping and reliable watch movements is performed by the Contrôle Officiel Suisse des Chronomètres, more commonly known as COSC.  A watch with a COSC certificate will be of high quality and not deviate more than -4 to +6 seconds a day.  A sign of a well made quality movement is the consistent timing rate +1 or -2 seconds a day and that whatever deviation is consistent rather than a wildly swinging deviation varying from day to day (eg. +1 one day, and -6 the subsequent day).



COSC tests watch movements from various manufacturers without a watch case and winding mechanism such that the testing and certification is completely blind.  COSC testing entails a 15-day period in with the watch movement five different positions and at three different temperatures and environmental conditions.  Only watches that pass the rigorous COSC testing can have ‘Officially Certified” on the dial.


Rolex sends all their movements to COSC for certification and are thus true Chronometers.  All modern Rolexes have dials indicating  “Superlative Chronometer – Officially Certified.” Other manufacturers such as Omega and Breitling also have some models Officially Certified on the dial after COSC certification, but Rolex sends all their movements for certification and every year tops the certification charges with the most movements passing.


So, yes a Rolex Daytona Chronograph is Officially Certified as a Chronometer –both important distinctions.

– Sheldon Smith