Tactics Trainer Ratings

Hi all: I've noticed in the comments on Tactics Trainer problems, people often say something about what the problem is rated at, but that it shows a different rating when I attempt to solve it. Do the problems ratings change based on how many people complete them?

I'm not sure if it is based on time, since sometimes I will fail a problem in ten seconds, then try it again and even after 3 minutes it still shows the same rating for me.

Then, sometimes it changes for me even on the second try!

What's up?

Yes, the problems are treated like a player with a rating. The tactic rating will increase or decrease depending the rating of the players that solve them.

http://www.chess.com/tactics/help#rating

thanks!