Returns the inverse hyperbolic tangent of a number. Number must be between -1 and 1 (excluding -1 and 1). The inverse hyperbolic tangent is the value whose hyperbolic tangent is number, so ATANH(TANH(number)) equals number.
Number is any real number between 1 and -1.
ATANH(0.76159416) equals 1, approximately
ATANH(-0.1) equals -0.10034