Modifications to chess sets enable a blind person to examine the position of the pieces on the board by touch.  The black squares are raised slightly above the level of the white squares.  The black pieces are distinguished by a small pin on the top.  Some boards have a hole drilled in the centre of each square and each of the pieces has a peg in its base which fits into the holes in the board.  Other boards use magnets to secure the pieces.  Each player uses a separate board and after making a move announces it to his/her opponent.