ATANH(x)
ATANH function calculates the inverse hyperbolic tangent of @x; that is the value whose hyperbolic tangent is @x. If the absolute value of @x is greater than 1.0, ATANH returns NUM! error. This function is Excel compatible.
ATANH(0.5) equals 0.549306. ATANH(0.8) equals 1.098612.
ATAN , TAN , SIN , COS , DEGREES , RADIANS