(1) A number having geodetic meaning and used frequently in geodetic calculations. Examples are the numbers defining a reference ellipsoid, the length of one degree of arc at the equator of a rotational ellipsoid, the rate of rotation of the Earth, the coordinates of the origin of a geodetic network, the force of gravity at Potsdam and the stadia constant. Sets of such numbers can be found in textbooks and professional journals. (2) One of a set of numbers adopted by the International Union of Geodesy and Geophysics (IUGG), on the recommendation of the International Association of Geodesy, and recommended for general use in geodetic calculations. The general use of such a set makes it easy to compare the results of various geodetic organizations and for one organization to use the results of another. If the numbers are changed frequently, they lose their usefulness. The IUGG therefore, except in recent years, has opposed frequent changes. Geodetic constants as of 1986 are given in the Appendix.