Metodi Metodiev, Petya Trifonova. "GEOMAGNETIC FIELD ELEMENTS OF THE BULGARIAN TERRITORY FOR 2020.0 EPOCH." SGEM International Multidisciplinary Scientific GeoConference EXPO Proceedings; 20th International Multidisciplinary Scientific GeoConference Proceedings SGEM 2020, Science and Technologies in Geology, Exploration And Mining (2020): 543-550. https://doi.org/10.5593/sgem2020/1.2/s05.069