With a single argument ERF returns the error function, defined as erf(x) = 2/sqrt(pi)* integral from 0 to x of exp(-t*t) dt. If two arguments are supplied, they are the lower and upper limits of the integral.
If either @lower_limit or @upper_limit is not numeric a #VALUE! error is returned.
This function is upward-compatible with that in Excel. (If two arguments are supplied, Excel will not allow either to be negative.)