SK-42 reference system

The SK-42 reference system also known as the Krasovsky 1940 ellipsoid, is a coordinate system established in the Soviet Union in 1942 as Systema koordinat (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. The coordinate  system  SK-42  served  as  a  foundation  for  developing  the SK-63 reference system   which   was   created   and   used   primarily   for   civilian   and   industrial   development   purposes.

The Krasovsky 1940 ellipsoid uses a semi-major axis (equatorial radius) $a$ of 6,378,245 m, and an inverse flattening $1/f$ of 298.3