Comparison between the S16 (blue) and WH07 (red) models of comparable main sequence mass, with s12 and s12A (top), s20p1 and s20A (middle), and s25p2 and s25A (bottom). In each panel, the flux is divided by the integral of the flux falling between 1000 and 25 000 Å (and then scaled by a factor of 10³), which is similar to forcing all models to have the same total decay power absorbed (in reality, the optical flux differs between models of the same mass because of the differences in ⁵⁶Ni or γ-ray escape; see Table 1). This normalization procedure also allows one to estimate by eye the cooling power of strong lines relative to the total decay power absorbed.