(1) You should do multiple trials in order to judge quality - one game is simply not enough to reach a conclusion.
(2) Rybka is an "outdated" engine. Stockfish and Komodo nowadays are the engines of choice, and their ratings are about 3300, which means that they will score 75%+ against a 3000 rated engine. The analysis engine for chess.com is Stockfish 8, which is much stronger than any version of Rybka. I believe computer level 10 is simply that engine on max strength.
(3) Each engine has a different evaluation algorithm, which will cause different moves to be played.
Hi,
I was playing a computer-assisted chess game against level 10 chess.com engine, as black, to see how strong it is. I have a quad core 64 bit PC, Windows 10, 8GB RAM. The engine I was using was Rybka 2.3.2a 64 on ARENA. This site gives the engine's approximate ELO rating as close to 3000:
http://www.computerchess.org.uk/ccrl/404/cgi/engine_details.cgi?print=Details&eng=Rybka%202.3.2a%2064-bit
I had created a time limit for my engine, 10 minutes for all the moves. The game was over in less than ten minutes, and I, playing black, got mated. It made me wonder if the chess.com engine is even stronger than 3000! But then I decided to not jump to conclusions and start with an analysis.
So I had Chess.com engine do 2minute analysis on the game, and it said one of my engine's moves was inaccurate. Here's the diagram, with black to move (r2q2k1/1bpp1pp1/3b1n1p/pp2r3/4PB2/PNP5/1PB2PPP/R2QR1K1 b - - 1 16):
The move I had made, with the suggestion of Rybka, was Re8. Chess.com suggested Rxe4. I thought maybe the time limit had caused my engine to make that mistake, so I gave it full 2 minutes to analyze this position and instead of Re8, which it had played, it now suggested Re6. Problem is that Chess.com engine suggests Rxe4. So now I thought maybe the Chess.com engine is wrong, but then when I tried couple of online sites that let you put Fen and they tell you next best move, three out of four also (almost instantaneously) suggested Rxe4, and only one suggesting Re6.
What do you think is going on? Why is the chess engine on my PC not functioning optimally? Is that been your experience too? I mean Chess.com level 10 makes moves like in 5 seconds, so time limit on my engine should not have been a major issue (though I even gave it 2 minutes for that position and still did not get it right). Hmmm.