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Chronograph vs. Chronometer. What’s the difference?

What is a Chronograph?

Though a chronometer may sound similar to a chronograph, they are actually quite a bit different. In short, a chronograph is a fancy word for a stopwatch or timer! A stop watch usually has three pushers, start, stop and reset. It’s important to take note that when the chronograph feature of the watch is in use it does not interfere with the functionality of the watch. The Fossil Crewmaster Sport Chronograph would fall under that litmus test.

What is a Chronometer?

Well, a chronometer is defined as an instrument for measuring time, especially one designed to keep accurate time in spite of motion or variations in temperature, humidity, and air pressure. Historically, because of the accuracy requirements with regards to widely changing spectrums in environmental conditions, chronometers were first developed for marine navigation.

Not only is a chronometer used as a time piece, a chronometers timepiece functionality is used in conjunction with astronomical observation to determine longitude. In Switzerland only timepieces certified by the Controle Official Suisse des Chronometres (COSC) may use the word Chronometer on the watch. A chronometer can be a chronograph, though not the other was around. Make sense?

What is a marine chronometer?

 John Harrison Watchmaker and inventor of the chronometer
John Harrison Watchmaker

A marine chronometer is a timepiece that is precise and accurate enough to be used as a portable time standard, it therefore be used to determine longitude by means of celestial navigation. John Harrison was born March 1693 and died March 24, 1776, in London, UK.

Latitude is distance north or south of the equator while longitude is distance east or west of the prime meridian. While latitude was an easier number to keep record of , there was no real accurate method to measuring and keeping an accurate record of longitude while at sea.

Obviously, accurate measurements of both longitude and latitude and other potential advances were of most interest to nations investing in long distance trade and outposts and settlements overseas. The ability for sea captains to determine their exact position at sea would mean that ships could travel more directly and speedily to their destinations with the potential to create commercial and strategic advantages.

Because of the commercial and military strategic advantages of an accurate measurement of longitude demanded, The Longitude Act of 1714 was created and passed by the Parliament of the United Kingdom in July of 1714. The act included a substantial monetary award for the individual that could find the easiest, effective and practical method for determining a ship’s longitude.

After Queen Anne ratified the ‘Act for Providing a Publick Reward for such Person or Persons as Shall Discover the Longitude at Sea’,  watchmaker John Harrison answered the call and invented the first practical marine chronometer, which enabled navigators to compute accurately their longitude at sea.

According to the COSC, the official definition of a modern chronometer is as follows:

  • A chronometer is a high-precision watch capable of displaying the seconds and housing a movement that has been tested over several days, in different positions and at different temperatures, by an official neutral body (COSC).
  • Each chronometer is unique, identified by a number engraved on its movement and a certification number given by the COSC.
  • Each movement is individually tested for several consecutive days, in 5 positions and at 3 temperatures.
  • Each movement is individually measured. Any watch with the denomination “chronometer” is provided with a certified movement.

Whereas the chronometer certification used to be a true mark of achievement for a watchmaker, in these days of precision mass-manufacturing there are tens of thousands of Swiss-made mass-produced movements which easily pass the modern chronometer certification testing.

So while chronometer certification is still an indication of a good-quality watch that keeps accurate time, it may not have the same cachet it once did. Today it really represents a minimum acceptable standard of performance for a quality mechanical timepiece.

John Harrison should be very proud.