| 21. | The marine chronometer was invented by John Harrison in 1730.
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| 22. | Thomas Mercer Chronometers still makes chronometers to the present day.
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| 23. | Thomas Mercer Chronometers still makes chronometers to the present day.
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| 24. | The line up also contains chronographs and COSC certified chronometers.
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| 25. | Slightly later, John Harrison would successfully build marine chronometers from 1730.
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| 26. | From 1818 the Admiralty began issuing chronometers to naval ships.
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| 27. | Further, the rates of all chronometers vary with time.
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| 28. | Most of the chronometers remained in this cabin throughout the entire trip.
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| 29. | He navigated with the Thomas Mercer chronometer he carried under his jerkin.
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| 30. | This practice became obsolete when the ship chronometer was invented.
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