Comparison of synthetic spectra (T_eff = 12 000 K, log(g) = 4.4, solar composition) calculated with the original Atlas12 code (thin black line) and our modified version including level dissolution (thick red line). The proper implementation of this effect allows us to exploit the region around the Balmer jump, which is an important indicator for the surface gravity, for quantitative spectral analysis, which is particularly important for the analysis of the MMT spectra given their spectral range (3600–4500 Å).