White 66 vs Black 242

The two setups

White: setup #66 B N N R K B Q R

King on the e-file, rooks on d, h, queen on the g-file; one 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 66 gives White +0.22 (Morozov Balance Index, 400M nodes).

Black: setup #242 B N R K Q B N R

King on the d-file, rooks on c, h, queen on the e-file; one 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 242 gives White +0.17 (Morozov Balance Index, 400M nodes).

Why the pair is balanced

At the deepest rungs (400M, 800M, 1.6B nodes) the evaluation is exactly 0.00 each time, reaching search depth 61.

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 ±8 cp.

For comparison, in symmetric play setup 66 gives White +0.22 and setup 242 gives White +0.17: with both sides on the same rank the first move is worth something. In this pair Black's own setup absorbs that edge completely.

White is not forced into a single path: the best first move is d4, and 2 first moves are within 10 cp of it.

Along the engine's main line (30 moves) the evaluation stayed within ±7 cp the whole way: the balance holds as the pieces come out, not only on move one.

Engine self-play agrees: 10 games, White won 0, drawn 10, Black won 0 (White scored 50.0%).

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: -5

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 +19, Black +43, difference -24. 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, 10 draws, 0 Black wins, White scored 50.0%.

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| 7 cp, mean 1.0 cp, final 0 cp.

Engine self-play

10 games at 500 000 nodes per move: White won 0, drawn 10, Black won 0 — White scored 50.0%. Average length 32.3 moves.

1. d4 e6 2. f3 f5 3. Nd3 O-O-O 4. O-O-O Nf6 5. b3 b6 6. h4 Nc6 7. Nc3 Nb4 8. e3 Kb8 9. Kb1 Nxd3 10. Bxd3 Rg8 11. e4 fxe4 12. fxe4 Bb4 13. e5 Ng4 14. Rf1 Rf8 15. h5 Qe7 16. Bxh7 Rxf1+ 17. Qxf1 Rf8 18. Qe2 Qg5 19. Nd1 Nf2 20. Nxf2 Qxg2 21. Rf1 Bf3 22. Qb5 Bc6 23. Qe2 Bf3 24. Qb5 Bc6 25. Qe2

1. e3 Nc6 2. d4 d5 3. Nd3 b6 4. O-O-O O-O-O 5. g4 f6 6. f4 e5 7. dxe5 fxe5 8. b3 exf4 9. exf4 d4 10. Bg2 Nf6 11. Nd2 Nd5 12. Kb1 Ne3 13. Re1 Be7 14. Nc4 Nxg2 15. Qxg2 Bb7 16. Qh3 b5 17. Nd2 Nb4 18. Nxb4 Bxh1 19. Nd3 Bb7 20. Nf3 Qd7 21. Nxd4 Rhe8 22. f5 Bb4 23. Rf1 a5 24. Ne6 Rxe6 25. fxe6 Qxe6 26. Bxg7 Be4 27. Bb2 Qg6 28. Rf6 Rxd3 29. Qf1 Rd2 30. Rxg6 Bxc2+ 31. Kc1 Bxg6 32. Qf6 Rd6 33. Qf3 Bd2+ 34. Kd1 Bc3+ 35. Kc1 Bd2+ 36. Kd1 Bb4+ 37. Kc1

Play it in the CH960 app

Open this page on a phone with the CH960 app installed, or find pair 66 / 242 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): bnrkqbnr/pppppppp/8/8/8/8/PPPPPPPP/BNNRKBQR w DHch - 0 1

Mirror twin: White 887 vs Black 615 — a different position (castling squares are fixed), not evaluated by the search.

Current place in the live balance rating: 293.