Counting explanation

Hej,

for https://www.littlegolem.net/jsp/game/game.jsp?gid=2467457 I need help with the specific counting (not relevant for the final result in this case).

The result in the chat log says B+13.5. The result in the info box says B+13.0. This in itself should not occur but I don't agree with either.

By my count it should be:

Black territory: 17
- black captured: 2

White territory: Depends on rules (points in seki) 2 or 0, the latter I presume
- white captured: 4
+ komi: 6.5

So by my count it should be, depending on ruleset, B+12.5 or B+10.5 but neither of the shown results.

Can someone point me how the difference occurs? Thanks.

I count 21 points for black - 17 territory plus the four white stones included.
White captured 2 stones and has no territory so 8.5 points with komi.
The result by Japanese counting should be 12.5 points for black.

Thank you, so the system was off. Is there any way to look into its reasoning?

Sorry for the formatting in the first post. I wasn't aware of textile and the conversion of leading plus and minus to indentation.

Luckily in go doesn't matter if you win by 12 or by 13 points.

Yes, of course, in this case it doesn't matter.

But from now on I will doubt and recount every game I win or lose with one or a half point...

My last finished game (19x19) also has the result displayed in the info rounded up, while the chat log displayed correctly the 0.5 points. Otherwise the result in the chat log is correctly counted.
This info box score is a recent problem, my game counted before last has both values correctly displayed.