Dutch class system
In the Netherlands, several clubs still use the 'class' system that was invented when go was first introduced in Europe In the class system, each player is assigned a numerical grade (a class). The stronger the player, the lower this number is. Every traditional kyu or dan grade is represented by two classes. Class 18 and 19 represent 1d, class 20 and 21 represent 1k, etc.
The classification committee, which assigns dan ranks to players based on their performance, also assigned these classes. This meant that a player could be promoted from 4d (class 13) to strong 4d (class 12). This was mostly used as an encouragement (an indication to the player that although his result were not yet sufficient for a full promotion to a new dan rank, they were also not far from it). This practice was abandoned in 2008, as the class system is falling into disuse (partly due to the availablity of the EGF rating system).
The number of handicap stones under this system is equal to (d+1)/2, where d is the difference in class. If this gets to a half number, say 4.5 stones handicap, komi (usually 6 points) is used to get to a full handicap.
- If two 1k players of class 20 meet (class difference 0), handicap is (0+1)/2 = 0.5 (black starts, 6 points for white)
- If a strong 1k (class 20) meets a weak 3d (class 15), handicap is (5+1)/2 = 3 (3 stones, no komi).
- If the same 1k meets a strong 3d (class 14), handicap is (6+1)/2 = 3.5 (3 stones, 6 komi for black, or 4 stones, 6 komi for white).
Traditionally, no handicap over 9 stones is given. Instead, black receives any remaining handicap as points (6 points per class)
- A weak 3d (class 15) plays a strong 15k (class 48). Handicap is (33+1)/2 = 17. Which translates to 9 stones and 16*6 = 96 points.
- A strong 1k (class 20) meets that strong 15k (class 48). Handicap is (28+1)/2 = 14.5. Which translates to 9 stones + 11*6 = 66 points.
See Points Rating System for the rating/handicapping system in use currently in Japan.
Anonymous: Some years ago the komi used was 5 points. The komi given to black in case of a 9+ stones handicap game was 5 points too. So a class 20/class 48 game translated to 9 stones and 55 points komi for black. Why the change of this "negative komi" from 10 points per kyu/dan grade to 12 points with the change from 5 to 6 points komi? (As far as I know the 5-6 poijnts komi change is based on statistics based on equal games only).
Herman: The thought is that komi is worth half a stone (if black passes for his first move, white starts the game. If 6 is a fair komi, then black should now need those 6 points to make it fair. So the difference between black starting and white starting is 12 points which is 2x komi). When we stop compensating with stones beyond the 9 handicap, the points given should be worth half a stone per step, hence the use of 6 points now, and 5 when komi was still 5. It is, however, completely true that komi really only says something about the value of the first move, not about the value of all handicap stones. Such values are not know (and are unlikely to ever be found exactly, I think). I do think that additional stones are not worth less points, but liekly more. With 9 stones, professional players generally lose by around 140 points, which would mean around 16 points per stone. But with 17 stones, it is considered quite a challenge to make any living group at all. I guess that somewhere around 20 stones, that really becomes impossible, so those 20 stones are worth 341 points (Japanese scoring), which is 17 per stone.
Anonymous: I'm not convinced. I agree handicap stones above 9 do have extra value because of the increasing synergy. It's too easy to say negative komi should be 6 of even higher however. Maybe it is better to get less handicap stones per grade after the normal 9 stones handicap? After all, komi is nothing more than a way to give both players equal chances to win the game.
Herman: I think it is very hard, at that kind of strength difference, to find any system that accurately gives both players equal chances. I think there is nothing wrong with giving 5 points per class, or 6 points per class, or giving additional stones. If the players in a club like one of those over the other, they should by all means use it. This page is descriptive, not proscriptive, and usage in different clubs/cities probably varies. You could also consider using the system used in tokyo clubs, which is more fine-grained and thus perhaps more likely to balance itself correctly over time.
BuggyMind: This is off topic, but I'm not convinced that handicap stones are more than linear. The highest handicap game I've seen a record of was 29 stones, plus 5.5 reverse komi, between a 1k and a 30k. W+18.5. (Vivi vs BruiserPM on DGS, if you want to look it up.)
 I mean linear in ranks. I agree that they're more than linear in point value, but I suspect that ranks are too. Thickness begets thickness, it's just that players who are ahead usually prefer to secure the win rather than try to slaughter everything.
tapir: Is this system still in use? (I remember similar systems where used in Germany as well at one point, it dates back to pre-war times.)
Herman: Yes, we currently use it for our club ladder in Groningen.
Someone: If a 9d gives a 30k a 450 negative komi, then the 9d could never win. However, if the 9d gives 38 handicap stones to the 30k, then the 9d would be able to play. Though, by theory, 450 negative komi and 38 handicap stones are equivalent.