I am looking to convert from the area under the normal (Gaussian)
curve from -Z to +Z to obtain the value of Z.  This is the inverse of
the erf function, which is available in labview (except base package).

The only thoughts I have to solve this is either:
(1) interpolating a set of data obtained from use of the erf function,
or
(2) doing a binary search / goal seek using the erf function until
satisfied with the precision.

I scratched my head and searched the internet for a few hours.  I
cannot think of a better solution that the two you posted.  It looks
like you are forced into the classic tradeoff of time or space.

The problem is that the error function (erf) is a "Special Function"
which means that its derivative cannot be expressed with more
elementary functions.  Thus, there is no way to find the inverse by
solving for the variable.  This leaves us with numerical approximation
methods.

Thanks for your response, and your effort!