The following from man atanh has an error. Should not refer tp acosh()
DESCRIPTIONThe 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, acosh() returns not-a-number (NaN) and
errno is set. Does anyone know where this is created. Regards, Jerry