* - Note: this will sweep the grid once and show the possible values for each cell based on the values in its row, column and box. It won't take account of the odd / even regions - that's up to you!

Tip: If you have narrowed down the possible values for a cell, enter them in the cell and the numbers will automatically be made smaller to accommodate these 'pencil marks'. They will be ignored by the 'undo moves' function, and, of course, hints for other cells won't take your pencil marks into account.