Houston’s Leader in Rolex Watches

Rolex Was Right On “Kew”


August 27, 2018





It all began a little over 100 years ago when Rolex was granted its first class “A” chronometer certificate. The first of it’s kind for a wristwatch. Kew A Rolexes are probably the most accurate Rolexes ever produced, yet I am willing to bet the vast majority of Rolex lovers have never heard of them. I must admit for many years I persisted in that category myself.

   Most, if not all watch aficionados, have heard of a chronometer certification signifying that a watch has been tested in various positions under different temperatures and certified to a certain accuracy.The Controle Officiel Suisse des Chronometres or COSC for short is the organization charged with testing and certifying chronometers. COSC began in its present form in 1973. Before that time from 1961 until 1973 there were various Bureaux Officiels de Control De La Marche Des Montres often known by their acronym B.O.s

   But prior to 1961 B.O.s were completely independent and the most prominent of these was the Kew Observatory, near London England, which was a subsidiary of the prestigious Greenwich Observatory.Watches tested at the Kew were subjected to a more rigorous set of tests and held to a higher standard due to the fact that the Kew Observatory was responsible for the certification of all Marine Chronometers issued to the Royal Navy. The precision of those Marine Chronometers was paramount to determine a ship’s position, or longitude, at sea, and could not deviate more than a few seconds a day without putting ship and crew in danger. A Standard test would endure for 15 days while a Kew Observatory test would last a gruelling 45 days. Therefore all watches with an “A” certification were known to be extremely accurate in all positions in a wide range of temperatures.   Rolex first Kew certification recorded an average daily rate of only plus one second per day.Before that a highly precise wristwatch was the thing of utopian dreams but with that certification Hans Wilsdorf proved that in terms of precision a Rolex wristwatch could rival the best of timepieces


   According to Rolex records they produced a 145 movements over the course of a long 4 year period to be submitted to the Kew Observatory for testing. 9 of the movements failed to obtain certification leaving 136 movements destined to become rare collectors items sometime in the future.

   The lion’s share of those 136 certified movements were marked “Rolex Kew A Tested” and were offered in boys SpeedKing stainless steel cases. However the records also revealed that 24 of the Kew certified movements were encased in 34mm 18K gold cases with a reference number of 6210, this being the year 1954.

   The 18K gold models were fitted with a unique dial containing the words “Observatory Tested” printed on the dial below Rolex Oyster along with “Kew A Certificate” above the small seconds dial at 6:00.

    But by the time all the Kew A watches were completed, Rolex was close to the end of production of the calibre 700 movement used in those watches. Henceforth all the developments used to obtain the Kew A rating were never used in production of subsequent movements.

    So what was the true purpose of all the time and resources exhausted to obtain such a prestigious certification such as the “Kew A” for so few movements for company like Rolex. Well, first off, we have to remember that in those days Rolex was still not “ROLEX”, the household word it is today.But the time and effort involved in reaching such a pinnacle of precision in a wristwatch movement, for the entire world to witness, just may have played a big role in making Rolex, “ROLEX”.