The SK-42 reference system also known as the Krasovsky ellipsoid, is a coordinate system established in the Soviet Union in 1942 as Systema koordinat (Russian: Система координат 1942 года), and provides parameters which are linked to the geocentric Cartesian coordinate system PZ-90. It was used in geodetic calculations, notably in military mapping and determining state borders.
References
SK-42 reference system Wikipedia(Text) CC BY-SA