It is well known that various diurnal and morphological features of the ionosphere reveal substantial departures from the normally simplified assumption of spherical symmetry at certain times of the day or at certain geographic locations. A radio ray passing through such an ionosphere must bear information about its horizontal gradients. The leading edge of a backscatter ionogram is formed by obliquely propagated radio rays of minimum time delay and hence is useful in deducing information about the ionospheric horizontal gradients. In this regard, the ionospheric electron density distribution is modeled by a locally quasi-parabolic layer with six parameters. This six-parameter space is known as the ‘ionostate.’ Our object is to seek the ‘best’ ionostate in the sense that the corresponding mean square error in group delay is a minimum. A computer program has been written to carry out the specified procedure. A number of sample calculations are presented and discussed.