SudokuTool.de - Tutorial

###### Introduction
SudokuTool wants to help you in solving arbitrary Sudoku puzzles. This tutorial does not provide an introduction to the Sudoku game and its rules. The tutorial focuces solely on the usage of the SudokuTool. If you are new to Sudoku, go to wikipedia.org or one of the various Sudoku sites out on the Web.
###### Acquiring new Sudokus
Basically you have two options to get new Sudoku puzzles into the tool. First off, you can create a new Sudoku with the New button. SudokuTool then creates a random new Sudoku puzzle which has exactly one solution. Secondly you can import a Sudoku from a text file simply by dragging the text file from somewhere and dropping it onto the SudukoTool. To import a Sudoku puzzle the text file must meet the following requirements:
• It must contain exactly 81 digits, no more, no less
• Preset cells are denoted by digit 1-9 empty cells by digit 0
• It does not matter if and how the digits are separated or if they are in one or multiple lines
• It does not matter how the text file is named or what extension it has
The following example would be a valid import format for SudokuTool:
```6 0 8 0 9 5 1 0 0
0 0 0 0 0 7 0 0 8
1 4 0 6 0 0 2 0 5
3 0 2 8 5 0 0 0 1
8 5 0 0 0 1 3 6 0
4 0 0 0 0 0 0 0 0
0 0 0 0 0 0 7 1 0
0 2 3 7 1 4 9 0 0
7 0 4 9 8 0 0 2 0```
With this feature it is easy to import the weekly Sudoku from your favourite newspaper into SudokuTool. By the way: To export a Sudoku puzzle you just click on a preset cell, keep the mouse button pressed and drag the Sudoku on the desktop where you can drop it in a new text file that is automatically created for you.
###### Solving Sudokus
First off you need to understand that SudokuTool can run in two modes (actually three, but the third one is just an additional feature and not an exclusive mode). The two modes are set and mark. In set mode you can set a digit on the currently selected cell in the Sudoku board. You will get an instant visual feedback if the number that you have just set is allowed at that cell or not.
In mark mode you are able to write small candidate digits in the current cell for the digits that you think are allowed for the current cell. This feature tries to simulate a common strategy in solving Sudokus on a paper by searching the allowed digits and writing them in the cell as so called pencilmarks.
Finally there is the hints mode. This mode does the marking automatically, meaning it checks all empty cells for allowed digits and marks them accordingly. The hints are updated each time a cell is set. Obviously in hints mode you cannot mark cells. Hints are shown in a different color.
Finally, if you are really desperate and cannot find a solution, you can let SudokuTool solve your puzzle by pressing the Solve button. This works only if the Sudoku is solvable, if it is not, you will not get any feedback.