How accurate is Chess Maniac's online rating estimator? After decades away from tournament play, I decided to play in an open tourney my child entered. Trying to gauge how my game might have changed during my time away, I found an online rating estimator at Chess Maniac. I was surprised to find that it estimated me 500 points stronger than my (USCF) rating - which actually went down about 60 points at the tournament. So, how accurate is this estimator?

Edit: I realize the Chess Maniac page in question is just an estimator. I'm looking for answers indicating that it tends to overrate or underrate players and by how much. If it doesn't have a tendency one way or another, I'd like to know that.
Absolutely inaccurate. ELO rating is determined by playing a whole game of chess, not by solving a few positions without any pressure.

Please play some online games for better estimate of your playing strength.