Differences between various observational estimates and the model result, over a grid of models with varying deposition energies and densities. The upper two plots compare to LTE CO mass estimates from Spyromilio et al. (1988) and Liu et al. (1992). The lower two plots are comparisons with NLTE CO estimates from Liu et al. (1992) and Liu & Dalgarno (1995). The dark grey shaded areas show the contours of 0.3 dex difference in CO mass and the light grey shaded areas show the 0.6 dex contours. ρ₀ = 4.88 × 10⁹ cm⁻³, and L₀ = 6.2 × 10³⁹ erg s⁻¹ are the density and deposition energy for the standard SN 1987A model.