game is to use the pieces to create as many horizontal lines of blocks as possible. When a line is completed, it disappears, and the blocks placed above fall one rank. Completing lines grants points, and accumulating a certain number of points or lines cleared moves the player up a level, which increases the number of points granted per completed line. In most versions, the speed of the falling pieces increases with each level, leaving the player with less time to think about the placement. The player can clear multiple lines at once, which can earn bonus points in some versions. It is possible to complete up to four lines simultaneously with the use of the I-shaped tetromino; this move is called a "Tetris", and is the basis of the game's title. If the player cannot make the blocks disappear quickly enough, the field will start to fill, and when the pieces reach the top of the field and prevent the arrival of additional pieces, the game ends. At the end of each game, the player receives a score based on the number of lines that have been completed. The game never ends with the player's victory. The player can only complete as many lines as possible before an inevitable loss. Since 1996, the Tetris Company has internally defined specifications and guidelines that publishers must adhere to in order to be granted a license to Tetris. The contents of these guidelines establish such elements as the correspondence of buttons and actions, the size of the field of play, the system of rotation, and others. Game pieces The pieces on which the game of Tetris is based around are called "tetrominoes". Pajitnov's original version for the Electronika 60 computer used green brackets to represent the blocks that make up tetrominoes. Versions of Tetris on the original Game Boy/Game Boy Color and on most dedicated handheld games use black-and-white or grayscale graphics, but most popular versions use a separate color for each distinct shape. Prior to the Tetris Company's standardization in the early 2000s, those colors varied widely from implementation to implementation. Scoring The scoring formula for the majority of Tetris products is built on the idea that more difficult line clears should be awarded more points. For example, a single line clear in Tetris Zone is worth 100 points, clearing four lines at once (known as a Tetris) is worth 800,