Kirby wrote:
Either way, it sounds like capturing the ko was a viable option - but I had no idea about calculating points per move, etc.
It was pretty much based on emotion/feeling
I'm surprised that you don't do this when evaluating trades like this. It's one thing when the ko involves some amorphous open area involving future thickness or moyo or whatever - I wouldn't know how to count that well either, that's down to judgment. But it's quite another when it's actually the life and death of a sealed-in group, then you can count very easily.
Since each stone involved is 2 points, you can just count tetris-like blocks of 5 stones and go "10, 20, 30, .." points quite rapidly. Doing that in this case it takes only a few seconds of effort to see that the raw territory swing is ~70 points. Then you can optimize further as Bill did and consider that ''a'' would be 7-9ish points in sente afterwards for white, and add that to the value. Also add a tiny bit value for black's outer wall being weaker, but it's pretty strong so not much. So ~80 points. Since the swing happens over 4 moves (1 for white to win the ko, 3 for black to win the ko), that's ~20 points per move.
And if you keep in mind the following rough values, that gives you a useful mental guide to how big the thing is:
Ordinary big opening move: ~12-15 points/move (~= fair komi * 2)
Unusually huge opening move (a critical move that completes a huge moyo, etc): maybe ~15-18 points, possibly a little higher sometimes, depends on how critical
Big-macro-endgame: ~7-10 points/move ("sente monkey jumps" into 4th line areas, some patterns involving capturing 2 stones on the side, giant second line hane-connects)
Middle-endgame: ~3-7 points/move (various second line kosumis, monkey jumps into 3rd-line areas, capture single second line stone with small or gote followups)
These are the same as "miai counting" values for moves, or another way to think of it is "how much would the opponent have to pay me in additional komi for me to be indifferent between making this move and passing?", if you happen to have some intuition for the latter.
I find it a very useful technique to get a rough sense of how big a local ko is. Or when to actually live with a tripod-like-group (with tripod-sized groups, they're often not quite big enough to create and live with right away, so deciding when is a tricky timing issue), or when to ignore a cut or atari that threatens some local garbage stones that are cashwise big but don't have a huge effect on outer influence or strength of the groups involved.
wins the ko, which is an approach ko, White gets 45 points in the marked area -- if I have counted correctly --, and later White has a 7 pt. sente at "a", if not something better. So let's count 52 pts. for White here.
