The following consecutive readings were taken with a level and a 4-metre levelling staff on a continuously sloping ground at common intervals of 30 m: 0.855(on A), 1.545m, 2.335, 3.115, 3.825, 0.455, 1.380, 2.055, 2.855, 3.455, 0.585, 1.015, 1.850, 2.755, 3.845 (on B). The RL of A was 380.500. Make entries in a level book and apply the usual checks. Determine the gradient of AB.