“…Such sensors are used in the monitoring of the rockfall near the village of Vrachesh, Botevgrad Municipality. axes are calculated using trigonometric formulas (Kostak, 1991;Avramova-Tacheva, et al, 1998;Kostak et al, 1998Kostak et al, , 2007Dobrev, Kostak, 2000;Dobrev et al, 2005Dobrev et al, , 2019Dobrev et al, , 2021Dobrev, 2010, Krastanov et al, 2010Kostov et al, 2018).…”