The General Isogonic Map of the Katanga for Epoch January 1, 1941

The general isogonic map of the Katanga, on the scale of 1:5,000,000, was prepared by using the observations of magnetic declination which were made at most of the triangulation-points established during 1919 to 1942 by the “Service Geographique et Geologique du Comite Special du Katanga.” The observations made by the Lemaire Mission (1899–1909) were also used. The declination-measures were made with the magnetic needles with which every theodolite in use by the Service is fitted. These measures were corrected as follows: