Syntax: Atan ( number )
numberAny expression that resolves to a numeric value.
Data type returned: Number
The arc tangent of a number is the angle (measured in radians) whose tangent is the specified number. The range of values returned by the Atan function is -(pi/2) to pi/2.
If Atan (x) = y, then Tan (y) = x.
Atan (x) = Atan (-x).
Atan (0) = 0 Atan (1) = .785398163
which is pi/4 radians, or 45 degrees.