Brain exercise with numbers for coffee breaks. Your goal is to get nine numbers arranged horizontally or vertically so that each numbers is shown only once. You need no mathematical skills, only power of deduction!

If you are a registered user of Playray and have logged in, you can start playing right away. In case you haven't registered yet, the game will assign you a random visitor nickname. A wavy line (~) will appear automatically before your name in order to inform other players that you are not a registered player. By this we make sure that your nickname won't be confused with those of registered users. Registration is completely free of charge.

After having logged in, you can enter the game lobby. From the drop-down list displayed in the lobby you can choose the level of difficulty for the game (i.e. the number of clues shown in the grid when the game starts). The top results of each level of difficulty are displayed above the clues options. After you have chosen a level of difficulty, click the "Start" button. Note that some levels of difficulty are accessible to the Registered users of Playray only.

You can quit the game and return to the front page of Playray by clicking the "Quit" button.

Sudoku is played on a 9*9 grid that has been divided into nine 3*3 regions. The objective of the game is to fill the blank squares with numbers 1 through 9 so that no row, column, or 3*3 grid contains the same number twice. Even though Sudoku deals with numbers, no calculation or arithmetic skills are needed in the game. In fact, Playray.s version of Sudoku can even be played using pictures instead of numbers.

Sudoku is based on reasoning, which means that the purpose of the game is not to place numbers in the grid arbitrarily and hope for the best. Of course the game can be played in that way, too, but sooner or later a player using such strategy will get in trouble. In this game careful consideration surely leads to better results.

In the beginning of the game there are some clues (i.e numbers) in the grid. These numbers can.t be removed or changed. The game can be played by using mouse or the combination of mouse and keyboard.

Mouse: Click the square to which you want to add a number or change one. After this a menu on the left side opens, and you will be able to choose a number for the square by clicking it. If you don.t want to add a number to the square, you can cancel the choice of square by clicking on the square again.

Mouse+Keyboard: Move the mouse pointer on the square to which you want to add a number. You don.t have to click the square. Then press one of the number keys 1 through 9 on the keyboard. The number of your choice will be added to the square you have selected by the mouse pointer. If you want to remove a number from a square, press 0 (zero) or spacebar.

This is not required, but if you like, you can mark the numbers you have already added to the grid as "certain" or "uncertain". These markings function as the player.s own notes and they have no influence on the game itself. This being so, the player can choose whether he/she uses the marking function or not.

By Mouse: Click the square of your choice with the right mouse button. The first click marks the square as "uncertain" (a small question mark symbol appears), the second click marks the square as "certain" (a small tick symbol appears), and the third click removes all markings from the square.

By Keyboard: Move mouse to the square of your choice. The Up Arrow key marks the square as "certain" and the Down Arrow key marks it as "uncertain". The Right Arrow and the Left Arrow keys remove the markings from the square.

Once there are no blank squares left, the computer checks whether all numbers are in right places. If there is nothing to correct, the game ends and the time counter on the right side stops. If some numbers in the grid are incorrect, they are marked in red and the game continues until all errors have been corrected.

During the game, a menu is displayed on the right side of the screen.

If you don't want to see the clock during the game, you can click the "Hide" options box under heading "Time". When you do this, time will be shown only after the end of the game.

The drop-down menu enables you to choose whether you want to play using numbers (the traditional way) or pictures. It is also possible to use a combination of numbers and pictures, and there are two different types of numbers you can choose from.

The "Guiding Lines" options box allows you to turn the guiding lines showing the position of the mouse in the grid on or off. The guiding lines indicate in which line, column, and 3*3 grid the mouse is.

The "Sounds" options box enables you to turn the game sounds on or off.

The "Empty" button enables you to empty parts of the grid. The function of this button depends on the prevailing situation in the game:

• If the grid is full but there are errors in it, the "Empty" button removes all wrong numbers from the grid and leaves the rest of the numbers in place.
• If there are squares that have been marked "uncertain", this button removes only them.
• If there are squares that have been marked "certain", this button empties squares that have not been marked.
• Only if there are no markings at all, this button empties the entire grid.

The "New Game" button starts a new game in a new grid.

The "Back" button takes you back to the Sudoku lobby.