WHAT IS A CHRONOMETER?

[david]

 A few weeks ago I began to study Celestial Navigation. At 70 years of age I have no current plans to take off in a boat with a compass, watch and sextant but I had a lifelong curiosity about how navigation  worked  and the  importance  accurate time played in the navigational process.  Most of my working life was spent in manufacturing as a machine designer ( mostly automated machinery) but I also spent nine years (1978-1987) running the CNC department. My interest in watches began, like most people on this forum, as a post career hobby and I plan to keep it that way.  In any case, I was often exposed to the sales hype from the major watch factories  advertising their watch as a "chronometer", at a higher price, as opposed to a general watch which sold at a lower price. The "chronometer" product often had numerous buttons and impressive looking dials that rival pin ball machines, but, as I found out, that was nothing but sales fluff and had nothing to do with the timing device being a chronometer. What actually makes a chronometer  different from other timing devices is  consistency. This does not necessarily mean that it reads the correct time.. A true chronometer  will gain or lose time at a consistent rate and not necessarily tell the "correct" time. If it is to be used for celestial navigation it will come with a  certification certificate showing the  (consistent) rate of gain or loss (fast or slow) over a given time period;  which is typically one month.  This is called  watch error (WE) and must be taken into consideration when calculating a position fix. For example, if the chronometer is four seconds fast per month, one second of time needs to be subtracted from the indicated time for the first week, two seconds subtracted on the second week and so on until the end of the voyage.   A chronometer must never be reset during a voyage due to the possibility of disrupting the timekeeping process.  The precise time is obtained by adding or subtracting the WE (watch error) to the time indicated on the clock or watch dial. Every second of time represents a difference in position of four miles  so losing or gaining a few seconds of time due to  resetting the  clock could be disastrous. According to what I have learned so far,  almost any quartz watch can provide the consistent rate of gain or loss making it suitable to use in celestial navigation.  For mechanical timekeeping devices this is not the case. The mechanical chronometers that were used for celestial navigation in the past were extremely expensive  and still are even if purchased used. Some of them are for sale on Ebay and cost several thousand dollars. That said  quartz controlled electronic devices offer more accuracy at a lower cost and to the best of my knowledge, mechanical chronometers are no longer made.

david

[oldhippy]

Google Harrison chronometer he is the person who invented the chronometer.

This is the official Swiss chronometer site.

https://en.wikipedia.org/wiki/COSC

These cheap modern things are nothing of the sort. I do not know how they get away with it under the trades description act.

[vinn3]

  the watch dealers got away with the same scam with " same scam" selling " railroad watches"  even selling a watch case with RR inscribed.   in the railroad era;  "many a man has lost his life,  trying gain lost time".  vin

[david]

This is a section from the "Official Swiss  Chronometer Site".

 Some German, Japanese, and even non-certified Swiss movements can surpass the normative requirements. The Japanese have largely abandoned the accolade, replacing it with in-house testing to a slightly more strict standard as with, for example, the Grand Seiko. On the other hand, the Germans have set up their own testing facility in Saxony at the Glashütte Observatory ^[2][3] where the DIN 8319 standards, which mirror the ISO standards used by COSC, are employed. At one time the French provided similar large scale testing at the Observatory at Besançon, however, today only a very few watches are currently tested there and carry the accolade "Observatory Chronometer."

david