A function giving the arc tangent of its argument in radians. The permitted range of the argument is from - to + infinity.
By convention, the result will be in the range -PI/2 to +PI/2 (-90 to +90 degrees).
If you know the tangent of the angle, this function will tell you the angle (in radians).
As the magnitude of the argument (tangent) becomes very large (approaches + or - infinity) the accuracy diminishes.
In the example below, radian_angle becomes equal to the angle (in radians) whose tangent is y.
You can convert the answer to degrees by using the DEG function. (The DEG function is equivalent to multiplying by 180/PI.) The example below is similar to the first one, but the angle is in degrees.