Hi Aaron, thanks for bringing the problem with Fig 17/21 of Starburst99 to our attention. You are right: they are identical, yet they should be somewhat different. Apparently Fig 21 and the associated data file is just a copy of Fig17. Fig 17 is correct. It is the a=3.3 case, whereas Fig21 should be a truncated Salpeter IMF with M_up=30. I don't know how it happened but it did happen. I note that the same problem exists for Fig23 as well. To summarize: Figs 21 and 23 are just copies of 17 and 19. If you are interested in these cases, you may want to rerun a Starburst99 model interactively. This has the additional benefit of using the updated stellar library of de Mello et al. (see our webpage), which may be important for a spectrum with fewer O stars. Sorry about the inconvenience and thank you for choosing Starburst99. Regards, Claus