You may notice that its reported in the text that the 'Mary Celeste' was sighted by the 'Dei Gratia' on one date in the text, and another on the chart. the reality is it was first seen on both the 4th and 5th December;
This anomaly is explained by the fact that their record keeping was based on "Civil Time", presumably EST of the day and also "Sea Time", the celestial time of the ships current location.
Prior to 1920, all ships kept solar time on the high seas by setting their clocks at night or at the morning sight so that, given the ship's speed and direction, it would be 12 o'clock when the sun crossed the ship's meridian.
It would of course have been easier to express times in GMT, however that was not adopted as a world standard until 1884.
The establishment of nautical standard times, nautical standard time zones and the nautical date line were recommended by the Anglo-French Conference on Time-keeping at Sea in 1917.
GMT is based on mean solar time (at Greenwich, UK) and has since been replaced by UTC based on quantum resonance and a consensus of clock keepers.
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