Starting from an ocean of squares with unknown contents you must mark all the squares with mines and reveal all the clear squares. You don't actually have to mark the squares with mines, but it is a lot easier if you do. Once you have cleared all the un-mined squares, any remaining mined squares will be marked for you.

If you left click on a mine, or auto-clear a square with a mine in it you lose. To help prevent accidents, you aren't allowed to auto-clear around a square unless the number of marked mines equals the number given in the square.

By choosing Settings ▸ Preferences from the menu you can change the size of the games. Larger sizes obviously take longer and require more concentration. Smaller games are more frantic. We provide Small, Medium, Large and Custom sizes.

Figure 4 The preferences dialog.

On the right hand side of the dialog there are three parameters for controlling the custom size. Horizontal and Vertical are the width and height of the desired grid in squares. The number of mines is - obviously - the number of mines you need to find. If this number is set too high or too low then the game becomes very easy. The number of mines is limited to slightly less than the total number of squares.

There is a check-box in the properties dialog entitled Use "I'm not sure" flags. If you enable this then, when right-clicking on a square, it cycles between the normal flags used to mark the square as mined, a flag with a question mark on it and no flag. This new flag is to help you with your reasoning, to mark mines you think might be a mine but aren't sure about. These flags have no effect on the game; you still have to use the appropriate number of red marker flags to be able to clear around a numbered square.

Figure 5 The sequence of flags when "I'm not sure" flags are enabled.

The other check-box in the properties dialog is entitled Use "Too many flags" warning. This feature will show you a warning when you have placed too many flags. This is disabled by default, as it provides so much hint that it could be considered "cheating".

If you get stuck - it is reasonably common to end up with two options that you can't logically resolve - then you can either guess, or ask for a hint. When you choose Hint from the Game menu a single square is revealed (plus surrounding squares if it is blank). The choice of square is random, but should be helpful. There is 10 second penalty added to your time whenever you use a hint.

If your score is in the top ten you will be shown the list of top scores and have an opportunity to change the name recorded in the high score table. You can also review the scores later by choosing Scores from the Game menu. The drop-down menu at the top of the dialog lets you look at the scores for other board sizes.

Figure 6 The high scores dialog.

Resizing the window makes the squares bigger or smaller to suit. If you want to make maximum use of the screen then there is a Fullscreen option under the Settings menu. You can also use the F11 key to toggle full-screen mode.

The game can be paused automatically when you start using another window, or paused by choosing Pause from the Game menu. The playing area is blanked so you can't think ahead while the clock is stopped. To start playing again press the button labelled "Press to Resume".