Hello to all! I'm trying to develop a routine (in ESO-MIDAS) similar to NEAT (Nebular Empirical Analysis Tool) or NEBULAR package from IRAF that, by inputting certain emission line ratios i could get the physical conditions of the nebula (like Te, Ne, ionic and elemental abundances). The thing is, since i don't have any education of atomic physics, i'm finding big problems to understand this. I've read a lot, but i still cannot understand simple stuff like, how to determine if the nebula is low, medium or highly ionized, and how to use the atomic data to get temperatures and densities. So please, if you are a expert in this area, i would be very appreciated if you could explain to me how this works. Thanks in advance. Kind regards, Iris.