Maa kumerusest ja refraktsioonist tingitud parand pikkuste ja kauguste mõõtmisel, correction applied in some geodetic work to take account of the divergence of the surface of the earth (spheroid) from a plane, correction value is the change in amplitude needed to bring signals from a curved surface measurement to the flat surface, in geodetic surveying we have to consider the error due to the curvature of the earth and the refraction as well