In the notation system common in tournament play, columns are labeled with the letters "A–O" and rows with the numbers "1–15". (On "Scrabble" boards manufactured by Mattel as well as on the Internet Scrabble Club, rows are lettered while columns are numbered instead.) A play is usually identified in the format "xy WORD score" or "WORD xy score", where "x" denotes the column or row on which the play's main word extends, "y" denotes the second coordinate of the main word's first letter, and "WORD" is the main word. Although it is unnecessary, additional words formed by the play are sometimes listed after the main word and a slash. When the play of a single tile forms words in each direction, one of the words is arbitrarily chosen to serve as the main word for purposes of notation.