Longitude from 1 at the equator to 0 at the poles, which measures how circles of latitude shrink from the equator to a point at the pole, so the length of a degree of longitude decreases likewise. This contrasts with the small (1%) increase in the length of a degree of latitude (north-south distance), equator to pole. The table shows both for the WGS84 ellipsoid with = and = . Note that the distance between two points 1 degree apart on the same circle of latitude, measured along that circle of latitude, is slightly more than the shortest (geodesic) distance between
Nautical time maritime usage, GMT retains its historical meaning of UT1, the mean "solar" time at Greenwich. UTC, "atomic" time at Greenwich, is too inaccurate, differing by as much as 0.9 seconds from UT1, creating an error of of a minute of longitude at all latitudes and which is at the equator but less at higher latitudes, varying roughly by the cosine of the latitude. However, DUT can be added to UTC to correct it to within 50 milliseconds of UT1, reducing the error to only . In practice, nautical times are used only for radio communication, etc. Aboard the ship, e.g.