HP 50g and z-scores

I am able to get from z-score to area under the standard normal curve using the UTPN function, but have been unable to find the inverse function. Any mavens out there? Thanks.

bump

I don’t have this calculator, but if the user’s guide is to be believed (p.17-16), the inverse cdf for the normal distribution is not implemented as an internal function. That page in the guide gives examples of writing numerical inversion functions for UTPN, though.