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How are the openings classified? As in, what does the 'A' stand for in A27 or the '16' in C16?
A00 [Start position] A10 [English] 1.c4 A20 [English: King's (1...e5)] 1.c4 e5 A30 [English: Symmetrical] 1.c4 c5 A40 [Queen's Pawn Game] 1.d4 A50 [Indian: 2.c4] 1.d4 Nf6 2.c4 A60 [Benoni: 3.d5 e6] 1.d4 Nf6 2.c4 c5 3.d5 e6 A70 [Benoni: Classical] 1.d4 Nf6 2.c4 c5 3.d5 e6 4.Nc3 exd5 5.cxd5 d6 6.e4 g6 7.Nf3 A80 [Dutch] 1.d4 f5 A90 [Dutch: 2.c4 Nf6 3.g3 e6] 1.d4 f5 2.c4 Nf6 3.g3 e6
Seems pretty random, B's and C's are kingpawn games
The only thing I know is the variations of one opening usually have the same letter... Otherwise I barely see logic in it.
Even I don't see the logic in it...
Btw.. A00 is the Ware opening AND the Amar opening, not the starting position, and both are completely different openings.
ECO openings is a system which is used to go systematical through the openings.
For that, we used A-E, to classify the starting moves. The 1-99 after the letter is where it is in the system. A big opening, lets say ruy lopez (1: e4 e5 2: Nf3 Nc6 3: Bb5) got alot of numbers, because it is a big opening. A lesser opening got less numbers because that there is not so many sidelines.
Openings not starting with 1: e4 or 1: d4 (english, birds and so on) (A00-39)
1: d4 without by 1: .. d5 or 1: .. Nf6. (A40-44)
1: d4 Nf6 without 2: c4 (A45-49)
1: d4 Nf6 2: c4 without g6 or e6. (A50-79)
1: d4 f5 (A80-99)
1: e4 without 1: e6, e5 or c5 (B0-19)
1: e4 c5 (B20-99) (A classic example of extremely big opening)
1: e4 e6 (C0-19)
1: e4 e5 (C20-99)
1: d4 d5 (D0-69)
1: d4 Nf6 2: c4 g6 with d5 grünfeld (D70-99)
1: d4 Nf6 2: c4 e6 (E0-59)
1: d4 Nf6 2: c4 g6 (without d5) (E60-99)
That's rather complicated, and not easy to understand at all...
Why are there so many variations anyways? And how do they arise?