Definition of NORMSINV:
A Microsoft Excel function that delivers the inverse of the cummulative standarized normal distribution. You enter the “probability that a value Z is up to…” and it returns that value Z (in terms of “sigmas”, because it is the standarized distribution with average 0 and sigma 1).
Example: NORMSINV(0.5)=0, NORMSINV(0.00135)=-3, NORMSINV(0.9772)=2. NORMSINV(0) and NORMSINV(1) will return error, because they correspond to – infinte sigmas and +infinte sigmas.