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Municipal Nautical Museum of El Masnou


Sundial, end of the 18th century

Sundial, end of the 18th century

Quadrant or diptych sundial. This portable folding pocket instrument used sunlight to tell the time and was very popular among sailors until the 18th century. It works by casting a shadow onto a prepared surface, while a small compass serves to orient the horizontal plane of the quadrant.

Two coordinates are needed to determinethe exact ship’s position: latitude (distance north-south from the equator) and longitude (distance east-west from the Greenwich meridian).

Calculating latitude was no problem thanks to instruments such as the sextant and octant and mathematical tables.

The problem was to find a reliable way to determine longitude, which was achieved by using clocks. High-precision marine chronometers were made from the second half of the 18th century onwards.

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