Interesting, thanks for sharing that. The AGA one seems to be similar to the geometrical rule based on comparing the number of points on the 9x9 board (81) with the corresponding number for the 19x19 board (361). One 9x9 point would be worth 4.46 points on the 19x19 board by this simple comparison.
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That may be the rationale behind it, but I don’t really know (I’m an EGF player, not an AGA player).
I based the Baarle system on the fact that in my experience, I can give 7-8 handicap stones on 9x9 to (category 1) raw novices and 6 handicap stones on 9x9 to (category 2) more advanced beginners who can play by the rules and score their games independently.
I’d say category 2 is about 30k EGF (adults who completed a real life beginners course of some six 1-hour sessions). I’m 3d EGF, so 6 stones on 9x9 would then correspond to about 32 ranks difference.
I don’t know how the AGA typically ranks category 2, but if a (say) practiced 4-5d AGA can give about 6 stones on 9x9 to a category 2 beginner, perhaps they would rank such players at around 20k? At least that would be consistent with the AGA 9x9 handicap system.
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Note the Cambridge handicaps (at least the 13x13 ones) are known to be generous to black in slow games, but are used in a quick tournament (10 mins sudden death) which favours white. So end up being pretty well balanced (4ds and 25ks have won).
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In my youth club (age 7-12), I try to anchor the ranks of more active weaker players based on their 9x9 handicap against me. If they beat me a couple of times on 6 handicap on 9x9, they get their first diploma (30k, category 2).
So I don’t really want our handicaps to be generous to black. These are “ranked” games, so I want handicaps to be fair to both colors.
We usually don’t use clocks in my youth club, but children usually play quickly. I estimate real life 9x9 games between children in my club typically last about 6 minutes. Either way, I’m playing fairly quickly against them (like not more than about 10s per move), because I don’t want them to get bored when playing against me.
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IME for most 7-12 year old children in my club (who play mostly against other children in that age range) it takes some 50-100 9x9 games to reach about 50% against me on 6 handicap on 9x9.
More active youth players in my club may play some 5 of such games per week, so they may get their 1st diploma (30k) within about half a school year. I estimate that roughly 1 in about 30 raw novices reach that level in my club, roughly 2 per year.
The more persistent of those may reach about 15k in a few years, which means they can win against me at 3 stones on 9x9, or at 6 stones on 13x13, or at 17 stones on 19x19 (according to our current handicap table).
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I’m trying to work out equivalence factors for handicap stones on different board sizes (9x9, 13x13, 19x19) for use in a rating system for my local Go club.
I’m inclined to go with factors of 4 for 9x9, 1.78 for 13x13 and 1 for 19x19. This is based on equivalent spacing between stones on each board (see photos above), assuming that a strong player will find it equally hard to play against a weaker opponent (16 ranks weaker) with 4 stones on 9x9, 9 stones on 13x13, and 16 stones on 19x19.
Does this seem reasonable?
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I’d say it depends. Do you and other club members have some experience giving large handicaps to novices on smaller boards?
Your factors are more or less what the AGA uses, which may be be tough for white at the larger handicaps (and thus lead to inflation of lower ranks). But it also depends on which rank your club/association typically assigns to novices. Is that closer to 20k or closer to 30k?
I think it would be good to verify such assumptions in practice.
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Thanks very much for your comments. I will try to do the verification you suggest.
I’ve given 5 stones on 9x9 to a beginner, others have also gone as far as 5 but no more than that on 9x9.
On 19x19 it’s more or less policy to give no more than 9 stones so the 16 stone handicap has not been tested. 13x13 hardly ever gets used 
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I always give 6 stones on 9x9 against total beginners and they usually have no chance against me (4k) unless very gifted.
Which roughly matches this from @gennan :
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You’re OGS 3k. I expect that with some practice you can give 6-7 handicap to raw novices on 9x9 (like @richyfourtytwo).
If that is the case, and you use a factor of 4 ranks per handicap stone on 9x9, those raw novices would be ranked at about 27k. Do you feel this is about right for raw novices, or is it too high/low?
On 19x19, I’ll go as far as 17 stones.
Here are two slow IRL 13 handicap games against an adult player whose level I’d estimate at about 15k EGF at that time, based on games like these (he’s much stronger than a raw novice, he can probably give 13+ stones handicap himself to a raw novice on 19x19):
With the factors I use in our club, I would give him 5-6 stones on 13x13 and 3 stones on 9x9. The factors I use are 6 for 9x9, 3 for 13x13 and 1 for 19x19.
In my (children’s) club most games are played on 9x9, 2nd is 13x13 and 19x19 is a distant 3rd. Only a few of the players are stronger than about 20k and willing to spend more than some 10 minutes on a single game.
On 9x9 I give the strongest players (about 15k) 3-4 handicap and they give 5 handicap to raw novices (who get 8 handicap against me).
Edit: The games I linked are 13 stones handicap, not 17. I adjusted the numbers accordingly
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By the way, in the children’s club I use a color system similar to the colored belts and patches used to express (youth) player levels in martial arts.
This is also reflected on the player cards and the handicap tables.
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Thanks very much, this is very useful. Your colour coded rating chart and cards are very nice!
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