Buttons within each cell are used to set and unset its symbols and colourings and to perform operations on that individual cell.
The little buttons
When a puzzle is loaded the user is presented with a grid showing the starting clues, and, for each of the unsolved cells, their nine possibilities. A typical starting grid is shown in Figure 1.
The symbols 1-9 and the letter "R" shown in small font in the unsolved cells are actually the labels of little buttons. When a button showing a number is clicked using the left mouse button, the number is removed and the button changes to the background colour of the cell. See below (the "R" button) about how to restore the symbol.
These little buttons are also used to set the solution for a cell. This is achieved by clicking with the right mouse button. When this is done all the little buttons in the cell lose their symbols and change colour to that of the cell's background. At the same time the selected symbol appears on a white background in large font in the centre of the cell. The little buttons which were labelled with the symbols 1-9 become inactive: clicking on them has no effect. A cell containing a solution set by the user then looks like the initial clues. However, even though the "R" button has lost its label, it is still active and can be used to reset the candidates.
If the button labelled "R" is clicked, even if the user has set a solution for the cell, all the little buttons are reactivated and appear with their symbols 1-9. This is obviously useful if an incorrect solution has been chosen.
When looking for patterns of symbols it can be helpful to colour individual buttons. One way this can be achieved is by use of the middle mouse button: click on a little button with the middle mouse button and it will be shaded with a the current default colour; click on it again and it will will revert to the background colour. See the section Colouring symbols for more information about this.
By employing the little buttons in the simple ways just described the program can be used as a notebook for solving Sudoku puzzles.
The large coloured rectangles in the centres of cells are also buttons, in this case menu buttons. Clicking on these areas pops up a menu of options that can be applied on the corresponding cell.
An example is shown in Figure 2. Here the user has clicked on a cell in the second row. Options can be selected by dragging down on the menu in the usual way.
The first option in the cell menu will automatically remove, for this cell, any candidates that are already set as answers in the cell's row. Other options do the same for the cell's columns and box, with the final option combining all three. This is equivalent to applying the Simple filter to a single cell. As with Simple filter any singles created in this process will be set.
The next menu item reveals the answer for the cell. Undo will clear it. The final menu item will change the background colour of the cell to help identify patterns in the grid.