We take AH, the actual number of handicap stones used. We take NH, the natural number of handicap stones. Then we calculate the co-efficient (C) for each game via the following rules.
- if AH < NH then C = 0
- if AH = NH then C = 1
- if AH = NH + 1 then C = 2
- if AH >= NH + 2 then C = 3
EXT is then the sum of: C times the SOS of the opponent.
See also EXR
The exact definition of AH is needed. I imagine that by default if a 3kyu plays a 4kyu, then AH has the value of 1.
Each SOS is the score at tournament end.