MANOUSSAKIS, Gerassimos, and Paraskevas MILAS. “On the Existence of Neutral Directions of the Normal Gravity Field”. Contributions to Geophysics and Geodesy 44, no. 1 (March 31, 2014): 41–60. Accessed August 16, 2025. https://journal.geo.sav.sk/cgg/article/view/105.