ZAHOREC, P., J. PAPČO, P. VAJDA, F. GRECO, M. CANTARERO, and D. CARBONE. “Refined Prediction of Vertical Gradient of Gravity at Etna Volcano Gravity Network (Italy)”. Contributions to Geophysics and Geodesy, Vol. 48, no. 4, Dec. 2018, pp. 299-17, doi:10.2478/congeo-2018-0014.