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It’s the 240th anniversary of John Arnold coining the term chronometer this year…I prefer to speak about a commemoration rather than an anniversary Arnold & Son does not date back to 1764 The brand was established in 1995 so there is quite a gap between the two.
So we don’t celebrate anniversaries but we commemorate certain dates In 1778 John Arnold submitted his pocket watch to the Royal Observatory in Greenwich to have its precision tested for marine chronometer certification The watch passed all the tests and over a year and a half the variation in rate was just two and a half minutes, which is an average of 05 seconds per day.
The requirements for today’s COSC chronometer certificate are between -4 and +6 seconds per day So Arnold’s watch was ten times more precise than the chronometers of today and a thousand times more precise than the pocket . Source