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 almanac tabulates celestial coordinates for 10-minute intervals for the use in aerial navigation. The Sokkia Corporation's annual "Celestial Observation Handbook and Ephemeris" tabulated daily celestial coordinates (to a tenth of an arcsecond) for the Sun and nine stars; it was last published for 2008. To find the position of a ship or aircraft by celestial navigation, the navigator measures with a sextant the apparent height of a celestial body above the horizon, and notes the time from a marine chronometer. That height is compared with the height predicted for a trial position; the arcminutes of height difference is how many nautical