Uh... post a diagram, please. For now, I'll use a chessboard editor to figure out what happened...
Well, that was... I don't know. Maybe you were temporarily crazy or something. I suppose it's just a blunder. Happens every now and then, I once let my queen get captured for free.
I would have played b4 to drive away the bishop.
Sorry, afraid I'm not getting it (doesn't that in fact win a pawn?).
Sorry, afraid I'm not getting it (doesn't that in fact win a pawn?).
If my memory serves me right, there's a knight, a bishop and a queen defending that particular square.
So Qxd5 would develop the queen and win a free knight.
13 .. Qxd5 14. Qxd5, Nxd5 15. Rxc5 Nxf4 16. exf4 Nd4
Nxf4 onwards is not so easy to see
Yep, I thought of that line while I was going to sleep last night (for some reason when I looked at it earlier I'd stuck the White rook on d1 instead of f1 so he'd be able to play Kf1 after Nxe2+ and win the knight back)... 
Anyway, giving Nxd5 a ?? seems a bit harsh...like you say, that sequence isn't any too obvious.
Actually, not just the bishop being unprotected but the fact that you can't play Kf1... 
Calculation Lecture by Grandmaster Igor Khenkin (2659):
http://www.youtube.com/user/MelbourneChessClub?feature=watch
If you need help, please contact our Help and Support team.
Hi!
I lost today a game which went 1.d4 e6 2.c4 d5 3.Nc3 Be7 4.Bf4 Nf6 5.e3 0-0 6.Nf3 c5 7.dxc5 Bxc5 8.cxd5 exd5 9Be2 Nc6 10.0-0 Be6 11,Rc1 Rc8 12.a3 a6 13.Nxd5?? where black won the exchange and eventually won.. I was the stupid white(i'm about 2000 my opponent was about 2300)....my question is-what are the best books(or more generally ways!) in your opinion for me to improve my calculation skills so that a disaster like the above will not happen again?
Thx,Yoni