The strain gauge unit: 1 – supporting frame; 2 – movable frame; 3 – bearing assembly; 4 – transverse beam; 5 – longitudinal bar; 6 – attachment; 7 – basic wheel; 8 – mechanism for changing a depth; 9 – transverse beam; 10 – longitudinal bar; 11 – strain gauge S-shaped compression-tension sensor C2H; 12 – working body; 13 – movable transverse beam; 14 – movable transverse beam; 15 – measuring unit for a depth of the working body; 16 – adjusting screw.