Plots showing the flux ratio [O III] λ 5007/Hβ, as a function of the following other line ratios for M83 SNRs, and also for ones in M31 (Galarza et al. 1999) and M81 (Lee et al. 2015): (left) [N II] λ 6583/Hα ratio; (center) [O I] λ 6300/Hα ratio; (right) [S II] λλ 6716, 6731/Hα ratio. These plots can be compared with corresponding figures in the shock modeling paper of Allen et al. (2008).