How exactly does the computer determine the ELO improvment (or worsening) on a given problem? It seems that on ones where there's 5-6 moves to solve, I get +2or3, but on ones where it's 2-3 moves and I miss it, it scores a -10 or more. There doesn't seem to be any rhyme or reason to how much improved or worsened my ELO is regardless of the ELO of the problem or the RD of the problem. I think if I get 4 moves then miss the last one, I should still get at least a +1 as opposed to a -10 or other form of partial credit. Particularly as some problems only require 1 move, and I'm left wondering exactly what the next part of the tactic is.