[Computer-go] Japanese byoyomi in SGF files (possible KGS Bug?)

Erik van der Werf erikvanderwerf at gmail.com
Sun Jul 28 05:42:14 PDT 2013

Hi All,

I was just looking at how Japanese byoyomi time information is stored in
sgf files. The spec at http://www.red-bean.com/sgf/properties.html tells us:

Property: BL (WL)
Function: Time left for black (white), after the move was made.
Value is given in seconds.

Property: OB (OW)
Function: Number of black (white) moves left (after the move of this node
played) to play in this byo-yomi period.

Now let's say we're playing in Japanese byoyomi, e.g., with 3 periods of
each 12 seconds. It's our turn, we think for 10 seconds and then make a
move. In this case I would have expected the game record to show that we
thought about it for 10s (2s left) using the BL/WL property. I.e. I would
have expected "BL[2]OB[3]"

However, this is not what's happening when I look at some sgf files I got
from KGS. What happens there is that after the move is made the clock
resets to 12 seconds (the time available for the next move), and that value
is stored in the sgf. So, once in Japanese byoyomi the sgf just shows a
long list of "BL[12]OB[3]", which in my opinion is not very informative
(all it tells us is that the move was completed within the period, but not
exactly how much time it took).

I'm tempted to think that this is a bug, but since it might also be a
difference of interpretation of the spec I'd like to hear what others
believe is the correct implementation.

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