Equator is commonly modeled as a sphere flattened 0.336% along its axis. This makes the Equator 0.16% longer than a meridian (a great circle passing through the two poles). The IUGG standard meridian is, to the nearest millimetre, , one arc-minute of which is , explaining the SI standardization of the nautical mile as , more than less than the geographical mile. The sea-level surface of the Earth (the geoid) is irregular, so the actual length of the Equator is not so easy to determine. "Aviation Week and Space Technology" on 9 October 1961 reported that measurements using the Transit IV-A
History of longitude European and North American longitude measurement campaigns in the 1850s and 1860s, resulting in improved map accuracy and navigation safety. Synchronization by radio followed in the early 20th century. In the 1970s, the use of satellites was developed to more precisely measure geographic coordinates (GPS). In the process of searching for a solution to the problem of determining longitude, many scientists added to the knowledge of astronomy and physics. History of longitude The history of longitude is a record of the effort, by astronomers, cartographers and navigators over several centuries, to discover a means of determining longitude. The measurement of