White 205 vs Black 870

The two setups

White: setup #205 Q N R B K N B R

King on the e-file, rooks on c, h, queen on the a-file; no bishop starts in a corner; the knights start on central files. Castling follows the Chess960 rule: king and rook end on the classical squares. In ordinary symmetric play setup 205 gives White +0.20 (Morozov Balance Index, 400M nodes).

Black: setup #870 Q R B K R B N N

King on the d-file, rooks on b, e, queen on the a-file; no bishop starts in a corner; the knights start away from the centre. Castling follows the Chess960 rule: king and rook end on the classical squares. In ordinary symmetric play setup 870 gives White +0.44 (Morozov Balance Index, 400M nodes).

Why the pair is balanced

At the deepest rungs (400M, 800M, 1.6B, 3.2B nodes) the evaluation never left ±1 centipawns of equality, reaching search depth 63.

Admission rule: |cp| ≤ 5 at four budgets up to 4 billion nodes, no one-sided drift along the ladder, and confirmation by two independent engines — Berserk and Lc0 — each below its own median on symmetric positions. The same corridor is required at every deeper budget (8 G, 16 G) at which the pair has been evaluated.

The shallow rungs agreed early: from 100 thousand to 128 million nodes the evaluation never left ±9 cp.

For comparison, in symmetric play setup 205 gives White +0.20 and setup 870 gives White +0.44: with both sides on the same rank the first move is worth something. In this pair Black's own setup absorbs that edge completely.

The engine's first choice for White is f3; the alternatives are slightly weaker but keep the game level.

Along the engine's main line (30 moves) the largest swing was 44 cp (around move 19), ending at +10 cp — the position stays playable for both sides.

Engine self-play agrees: 10 games, White won 0, drawn 8, Black won 2 (White scored 40.0%).

Verification ladder

Nine independent searches of the starting position, each with a larger node budget. Evaluation in centipawns from White's point of view.

Deep verification

The search ladder reaches 1.6 billion nodes; admission needs a 4-billion rung and two further engines on top of that. Beyond even that, every pair was re-checked at budgets up to ten times larger and in thousands of self-play games. This section shows what each check returned for this pair.

This pair stays within the ±5 cp corridor up to 4 000 000 000 nodes.

Independent engines, run on the same position:

• Berserk 14: 0
• Lc0 0.32.1: +1

Independent confirmations: 3 of 3. An engine counts as confirming when its reading of the pair is closer to equality than its own reading of a typical symmetric Chess960 position (+10 for Berserk, +18 for Lc0). Where only one engine confirms, the pair is balanced according to that engine alone, and this page says so.

Own weight of each setup, measured against the classical array: White -15, Black +48, difference -63. A balanced pair needs White's setup to be weaker by about the price of the first move.

Extended self-play: 10 games, 0 White wins, 8 draws, 2 Black wins, White scored 40.0%.

Best first moves

The 3 best first moves for White, searched together at 400 000 000 nodes.

Main-line play-out

30 moves, 5 000 000 nodes per half-move. Largest |evaluation| 44 cp, mean 27.4 cp, final +10 cp.

Engine self-play

10 games at 500 000 nodes per move: White won 0, drawn 8, Black won 2 — White scored 40.0%. Average length 47.6 moves.

1. f3 b5 2. b3 f5 3. c4 bxc4 4. Ne3 e6 5. Nxc4 Nf6 6. a3 Ng6 7. b4 e5 8. Be3 Ba6 9. Qa2 e4 10. O-O f4 11. Bf2 Qd5 12. Bb3 Qg5 13. Nc3 Nh4 14. Bxh4 Qxh4 15. Nxe4 Nxe4 16. fxe4 Rxe4 17. e3 Bxc4 18. Rxc4 Rxc4 19. Bxc4 Bd6 20. Bd3 c6 21. Qg8+ Kc7 22. Qxg7 fxe3 23. g3 Qe7 24. Qxe7 Bxe7 25. dxe3 h6 26. Rf7 Bg5 27. Kf2 Re8 28. e4 Rb8 29. Rf5 Bc1 30. Ra5 Rf8+ 31. Kg2 Kb6 32. a4 Rf6 33. e5 Re6 34. Bf5 Re7 35. Rc5 Ba3 36. Rc4 Rxe5 37. Bxd7 c5 38. b5 Ka5 39. Kf3 Bb2 40. Bc6 Bd4 41. Be4 Re7 42. h3 Rf7+ 43. Kg4 Rg7+ 44. Kf4 Rf7+ 45. Bf5 Re7 46. h4 Re3 47. g4

1. f3 b5 2. Ng3 e6 3. Bf2 f5 4. O-O Nf6 5. e4 Ng6 6. b3 fxe4 7. fxe4 Nxe4 8. Nxe4 Qxe4 9. Bf3 Qe5 10. Qxe5 Nxe5 11. Be4 Bb7 12. Bxh7 Be7 13. Bg3 Ng4 14. d4 O-O-O 15. Nd2 Ba3 16. Rce1 Bb2 17. Rf4 Nh6 18. Bd3 g5 19. Rff1 Bxd4+ 20. Bf2 Bc3 21. Re2 a6 22. Ne4 Bxe4 23. Rxe4 d5 24. Re2 e5 25. Re3 Re6 26. Be2 b4 27. Rg3 Rg8 28. a3 a5 29. axb4 axb4 30. Rd3 c6 31. Rh3 Kb7 32. Bc5 Bd4+ 33. Bxd4 exd4 34. Bd3 Rg7 35. Rg3 Re3 36. Rxe3 dxe3 37. Rf6 Ng8 38. Re6 d4 39. Kf1 Kc7 40. Re4 c5 41. Bc4 Rg6 42. Ke1 g4 43. Re8 Nh6 44. Re7+ Kb6 45. Bd3 Rf6 46. Be4 Nf7 47. Rb7+ Ka6 48. Rb8 Rf2 49. Rg8 Ka5 50. h4 gxh3 51. gxh3 Nd6 52. Bd3 Kb6 53. h4 Rh2 54. Rg6 Kc6 55. Rg4 Nf7 56. Rg6+ Kd7 57. Rg7 Ke7 58. Bc4 Rf2 59. Rh7 Ke8 60. Be2 Nd6 61. Rh5 Nf5 62. Kd1 Ng3 63. Bb5+ Kf8 64. Re5 Rh2 65. Kc1 Rxh4 66. Bd3 Rh1+ 67. Kb2 Rh5 68. Re6 Nh1 69. Bg6 Rg5 70. Re8+ Kg7 71. Bd3 Nf2 72. Bc4 Kf6 73. c3 bxc3+ 74. Kb1 Rg1+ 75. Kc2 Rg2 76. Rf8+ Ke7 77. Rc8 Ng4+ 78. Kd1 Ne5 79. Rxc5 Nxc4 80. Ke1 d3 81. Rc7+ Kd6

Play it in the CH960 app

Open this page on a phone with the CH960 app installed, or find pair 205 / 870 in the app's encyclopedia, then choose how to play.

• Local game — two players on one device, with a clock.
• With a mentor — a clearly labelled training bot with hints, at your level.
• Challenge a friend — an online game by link; both players get the same pair, colours swap on rematch.

Play this pair against the computer, right here Play a friend

FEN (Shredder, castling rights by rook files): qrbkrbnn/pppppppp/8/8/8/8/PPPPPPPP/QNRBKNBR w CHbe - 0 1

Mirror twin: White 664 vs Black 86 — a different position (castling squares are fixed), not evaluated by the search.

Current place in the live balance rating: 47.