The arctan function is used to obtain an angle from the tangent trigonometric ratio, which is the ratio between the side opposite to the angle, the rise, and the adjacent side, the run, of a right angled triangle.
Or in a simpler form, the arctan function can be used to calculate the angle of a slope by dividing the rise by the run measurement.
Atan ( rise ÷ run) the rise = 11 feet the run = 25 feet 11 ÷ 25 = 0.44 Atan ( 0.44 ) = 23.74949449°