Checkers is played by two persons who oppose each other across a board of 64 light and dark squares, the same as a chessboard. The 24 playing pieces are disk-shaped and of contrasting colours (whatever their colours, they are identified as black and white). At the start of the game, each contestant has 12 pieces arranged on the board. While the actual playing is always done on the dark squares, the board is often shown in reverse for clarity. The notation used in describing the game is based on numbering the squares on the board. The black pieces always occupy squares 1 to 12, and the white pieces invariably rest on squares 21 to 32.