Lately my chess calculation breaks down in the range of six to eight half-moves. Either I overlook important branches at that point, or I simply cut off the line. Case in point: last fall in a game against Avraam Pisminneyy, I calculated eight forcing half-moves and then rejected a line, when in fact mate was forced in two more half-moves. My “event horizon” manifested itself again tonight, when I made a couple of crucial errors in calculation right in that same range.
Slater (2035) – Shmelov (2391)
1.e4 e6 2.d4 d5 3.Nc3 Nf6 4.Bg5 Be7 5.e5 Nfd7 6.Bxe7 Qxe7 7.f4 a6 8.Nf3 c5 9.dxc5 Nc6 10.Qd2 Qxc5 11.0-0-0 b5 12.Ne2 b4 13.Ned4 a5 14.f5 Nxd4 15.Nxd4 Qe7
Here’s the first calculation error. I rejected 16.Nc6 because of the strange line 16…Qh4 17.g3 Qh6 18.Qxh6 gxf6 and now he’ll kick my knight and win my e5 pawn. Overlooked: The incredibly simple 19.Re1. After the game Denys said black’s prospects are dim in that position. (He thought 16…Qh4 was ridiculous and was planning 16…Qc5 with a probable repetition because he didn’t like 17.Nd4 Qb6 18.Qg5.)
Second error: After 16.fxe6 fxe6 17.Nf5 exf5 18.Qxd5 Rb8
Now 19.Bb5 is better but I played 19.e6. Great fun is 19.e6 Nc5 20.Bb5+! Rxb5 21.Qc6+ (splat!) and I believed black also to be busted after 19.e6 Nf6 20.Bb5+ Kf8 21.Qd8+ Ne8 22.Bxe8 Qxe8 23.Qd6+ forking the rook on b8. What I missed was instead 22…Qxd8 23.Rxd8 Ke7 and the best white can do is 24.Rxc8 Rxc8 25.Bf7, which we agreed after the game is probably lost for White.
So after 19.e6 Nf6 20.Bb5+ Kf8, I discovered that defensive resource and varied with 21.Qxf5, just trying to further denude his king, but he calmly untangled and retained his winning material advantage.
So here’s the point. It’s easy and formulaic to say “I need to get better tactically,” but more helpful to be more specific. In my tag post I mentioned Kotov’s calculation exercise. The analysis tree method is particularly helpful for measuring and stretching your event horizon. Knowing the average depth (i.e. how many moves into the calculations) at which I’m making tactical errors or cutting off my analysis, I can do the exercise with a very specific task: “Must calculate all branches out to ten half-moves”. If through repetition I manage to start hitting that mark with reasonable breadth and accuracy, I can push on to twelve half-moves. Try it.