  We examine the accuracy of a common FIP effect diagnostic, the ratio of Ne VI
to Mg VI lines in the solar transition region. Since the two ions have quite
similar contribution functions near their maxima in equilibrium, the ratio of
these two ions is often taken to be the abundance ratio of Ne and Mg. First we
compute non-equilibrium ionization effects on the ratio f(Ne+5)/f(Mg+5) of ion
fractions for a variety of simple flows through the transition region.
Calculating the spectral line ratios for a few examples, we then show that
non-equilibrium effects as well as temperature and density dependence must be
evaluated for each line ratio used in the diagnostics.
