ATAN Returns the arctangent, or inverse tangent, of a number. The arctangent is the angle whose tangent is number. The returned angle is given in radians in the range -pi/2 to pi/2.
Syntax
ATAN(number)
Parameters
Number – The tangent of the angle you want.
Return Value
Returns the inverse hyperbolic tangent of a number.
Reference Data
https://docs.microsoft.com/en-us/dax/dax-function-reference