Ha, finally my registration could be processed manually, as all automatic procedures consistently failed. So this thread is now also open to me for posting. Let me start with some remarks to the ongoing discussion. * I tried Reinhards 4A vs 8N setup. In a 100-game match of 40/1' games with Joker80, the Knights are crushed by the Archbishops 80-20. So although in principle I agree with Reinhard that such extreme tests with setups that make the environment for the pieces very alien compared to normal Chess could be unreliable, I certainly would not take it for granted that his claim that 8 Knights beat 4 Archbishops is actually true. Possible reasons for the discrepancy could be: 1) Reinhard did not base his conclusion on enough games. In my experience using anything less than 100 games is equivalent to making the decision by throwing dice. It often happens that after 30 games the side that is leading by 60% will eventually lose by 45%. 2) Smirf does not handle the Archbishop well, because it is programmed to underestimate its value, and is prepared to trade it to easily for two Knights to avoid or postpone a Pawn loss, while Joker80 just gives the Pawn and saves its Archbishops until he can get 3 Knights for it. 3) The shorter time control used does restrict search depth such that this does not allow Joker80 to recognize some higher, unnatural strategy (which has no parallel in normal Chess) where all Knights can be kept defending each other multiple times, because they all have identical moves, and so judges the pieces more on their tactical merits that would be relevant for normal Chess. * The arguments Reinhard gives against more realistic 'asymmetrical platesting': | Let me point to a repeatedly written detail: if a piece will be | captured, then not only its average piece exchange value is taken | from the material balance, but also its positional influence from | the final detail evaluation. Thus it is impossible to create | 'balanced' different armies by simply manipulating their pure material | balance to become nearly equal - their positional influences probably | would not be balanced as need be. seem invalid. For one, all of us are good enough Chess players that we can recognize for ourselves in the initial setup we use for playtesting if the Archbishop or Knight or whatever piece is part of the imbalance is an exceptionally strong or poor one, or just an average one. So we don't put a white Knight on e5 defended by Pf4, while the black d- and f-pawn already passed it, and we don't put it on a1 with white pawns on b3, c2 and black pawns on b4, c3. In particular, I always test from opening positions, where non of the pieces is on a particularly good square, but they can be easily developed, as the opponent does not inderdict access to any of the good squares either. So after a few opening moves, the pieces get to places that, almost by definition, are the average where you can get them. Secondly, when setting up the position, we get the evaluation of the engine for that position telling us if the engine does consider one of the sides highly favored positionally (by taking the difference between the engine evaluation and the known material difference for the piece values we know the engine is using). Although I would trust this less than my own judgement, it can be used as additional confirmation. Like Derek says, averaging over many positions (like I always do: all my matches are played starting from 432 different CRC opening positions) will tend to have avery piece on the average in an average position. If a certain piece, like A, would always have a +200cP 'positional' contribution, (e.g. calculated as its contribution to mobility) no matter where you put it, then that contribution is not positional at all, but a hidden part of the piece value. Positional contributions should average to zero, when averaged over all plausible positions. Furthermore, in Chess positional contributions are usually small compared to material ones, if they do not have to do with King safety or advanced passers. And none of the latter play a role in the opening positions I use. * Symettrical playtesting between engines with different piece-value sets is known to be a notoriously unreliable method. Dozens of people have reported trying it, often with quite advanced algorithms to step through search space (e.g. genetic algorithms, or annealing). The result was always the same: in the end (sometimes after months of testing) they obtained piece values that, when pitted against the original hand-tuned values, would consistently lose. The reason is most likely that the method works in principle, but requires too many games in practice. Derek mentioned before, that if two engines value certain piece combinations differently, they often exchange them for each other, creating a material imbalance, which then affects their winning chances. Well, 'often' is not the same as 'always'. For very large errors, like putting AR the undervaluation of A only can lead to much more complicated bad trades, as you have to have at least two pieces for A. The probability that this occurs is far smaller, and only 10-20% of the games will see such a trade. Now the problem is that the games in which the bad trades do NOT happen will not be affected by the wrong piece value. So this subset of games will have a 50-50 outcome, pushing the outcome of the total score average towards 50%. If A vs R+N gives you 60% winning chance,(so 10% excess), if it is the only bad trade that happens (because you set A slightly under 8), and happens in only 20% of the cases, the total effect you would see (and on which you would have to conclude the A value is suboptimal) would be 52%. But the 80% of games that did not contribute to learning anything about A value, because in the end A was traded for A, will contribute to the statistical noise! To recognize a 2% excess score in stead of a 10% excess score you need a 5 times lower statistical error. But statistical errors only decrease as the SQUARE ROOT of the number of games. So to get it down a factor 5, you need 25 times as many games. You could not conclude anything before you had 2500 games! Symmetrical playtesting MIGHT work if you first discard all the games that traded A for A (to eliminate the noise they produce, and they can't say anything about the correctness of the A value), and make sure you have about 100 games left. Otherwise, the result will be garbage.