tactics

Why do the numbers in "tactics trainer" seem random. I solve a pussle quickly and my tt rating goes down. I fail on a puzzle and my tt rating goes up. My % also jumps up and down unrelated to my performance.

The randomness is built in to try to add further confusion -

making the tactics training more challenging.

It depends on the score you get. If you get 4 out of 5 moves, you have 80% as a base. Then you have to factor in the time. If after time is factored in, and you have a score of above about 60%, then you'll gain points.  If it is below that, you'll most likely lose points. 

Failing and solving puzzles are completely different.  If you get 4 out of 5 moves but make a mistake on the fifth move, as shown above, you can gain points.  However, solving a tactic means that you must complete every move. You can solve a puzzle and go down in points because the time must be factored in.

That is all nice to know, but the important thing to get out of tactics is not the rating, it is the understanding of tactical themes.  Just do a couple thousand tactics and you'll end up with, not only an understanding of the system, but a decent rating.