Chronometer - article about Chronometer

Chronometers and chronographs are often confused, and are names sometimes used interchangeably. They are in fact two completely different devices, however. A chronograph is basically a stopwatch, or any instrument that is designed for measuring elapsed time. Chronometers on the other hand are highly accurate watches, and are not meant for measuring the duration of a specific event.

The ability to tell time accurately while at sea may not sound like a big deal, but it was a major breakthrough for ocean navigation, allowing for a high standard of accuracy for maps and greatly reducing the risks of getting lost at sea or running into dangerous waters. Prior to Harrison’s invention, navigation at sea was based on ‘dead reckoning’, which allowed a sailor to determine a vague latitudinal position based on the position of the stars, but gave no insight to his longitudinal position whatsoever. By using a sextant to gauge the position of the sun or stars, you can determine what time it is where you are locally. Then, if you have an accurate time keeping mechanism based on the time in some other location, you can determine your distance from that location.

So the first chronometers did just that; they kept an accurate measurement of the time in a designated location, which was always Greenwich, England as a standard. Then as sailors traveled they could measure the longitudinal distance they had gone by comparing local time to time in England. Harrison’s first inventions were very large and suffered from slight inaccuracies that became apparent on longer voyages. Eventually he produced a small and highly accurate model called the ‘H4’, which was the worlds first pocket watch, an invention that eventually led to today’s wristwatches.

Mechanical chronometers advanced over the years, but used the same basic weighted beam idea Harrison invented until the 20th century, when the discovery of the microchip and quartz time keeping movements rendered his ideas basically obsolete. Today, chronometers actually used in navigation are electronic, and function with GPS satellite support.

Now the word chronometer doesn’t mean what it used to. Any time keeping mechanism that meets the standards of the Swiss Official Chronometer Testing Institute (designated COSC based on the organizations French name) is a chronometer. What that basically means is any watch that meets a high standard of accuracy under an array of conditions, including different pressures, temperatures, and even under water, is officially labeled as a ‘chronometer’.

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