Returns the arctangent of a number. The arctangent is the angle whose tangent is number. The returned angle is given in radians in the range -p/2 to p/2.
Number is the tangent of the angle you want.
To express the arctangent in degrees, multiply the result by 180/PI( ).
ATAN(1) equals 0.785398 (p/4 radians)
ATAN(1)*180/PI() equals 45 (degrees)