SGN (Function)

is a function which takes one numerical parameter, and returns the 'sign' of the number.

If the parameter is zero,  returns zero. If the parameter is positive, then  returns 1, and if the parameter is negative,   returns -1. As such, when the parameter is nonzero,  evaluates to the same as  ... except when   is the 'buggy' value -0.

If the parameter is missing, the system produces, if the parameter is a string, the system givs a   error, and if two or more parameters are passed, the system gives the misleading   error.