Scrabble of points for each lettered tile is based on the letter's frequency in standard English; commonly used letters such as vowels are worth one point, while less common letters score higher, with Q and Z each worth 10 points. The game also has two blank tiles that are unmarked and carry no point value. The blank tiles can be used as substitutes for any letter; once laid on the board, however, the choice is fixed. Other language sets use different letter set distributions with different point values. Tiles are usually made of wood or plastic and are square and thick,
Tile-matching video game game mechanic, rather than a distinct genre of games. The mechanism of matching game pieces to make them disappear is a feature of many non-digital games, including Mahjong solitaire and Solitaire card games. Jesper Juul traces the history of tile-matching video games back to "Tetris" and "Chain Shot!", published in 1984 and 1985. While both focus on pattern matching, they differ in important design points such as time pressure, tile manipulation and match criteria. A second generation of influential matching games – "Puzznic", "Columns", "Dr. Mario" and "Plotting" – was published in 1989 and 1990. Games building on "Dr. Mario"'s