Longitude Act passed in July 1714. For details on many of the efforts towards determining the longitude, see History of longitude. The Longitude Act offered a series of rewards, rather than a single prize. The rewards increased with the accuracy achieved: £10,000 (worth over in ) for anyone who could find a practical way of determining longitude at sea to an accuracy of not greater than one degree of longitude (equates to at the equator). The reward was to be increased to £15,000 if the accuracy was not greater than 40 minutes, and further enhanced to £20,000 if the accuracy was not
Nautical mile of latitude is not constant, but about at the poles and at the Equator, with a mean value of . Other countries measure the minute of arc at 45 degrees latitude, giving the nautical mile a length of . In 1929, the international nautical mile was defined by the First International Extraordinary Hydrographic Conference in Monaco as precisely 1,852 metres. Imperial units and United States customary units used a definition of the nautical mile based on the Clarke (1866) Spheroid. The United States nautical mile was defined as based in the Mendenhall Order foot of 1893. It was abandoned in