I'll take a last shot and maybe someone can correct me if I'm wrong haha. Best way I can think to describe is using GPA as an example. Everyone knows the linear scale they use to give you a score for GPA (you see this score on your letter) with the 4.0 = 15/15, 3.9 = 14/15 and so on. The z-score would give you a different number for GPA because they give you a score based on the other applicants, i.e. if there was no one who they interviewed with a GPA lower than 3.6 then if you get a different score than the linear one because it kind of moves the scale up?