You can undo all the way back to the beginning of the puzzle (unless you have loaded a puzzle which was partially completed). There is only one new puzzle per level per day but you can play more from archives for the last two weeks. All these puzzles are solvable by pure logic. Here you can generate a puzzle at the required level of difficulty. Please note that the menu options are arranged a little differently in the Flash version. In the Active Number mode, all pencil functionality remains the same as does the ability to use the keyboard. To change the active number, select a new one from the Number Pad or scroll the mouse wheel down/up to increase/decrease the number. Those that prefer to solve by focusing on one specific number at a time will find this mode much more convenient. This is the reverse of the 'cell select' mode, where you highlight a cell and then select the number to input. The mouse cursor will change to this number and clicking on any cell will enter it in that cell. If you select this mode (via Edit->Preferences menu option), then the number you click from the Number Pad on the right becomes the 'active number'.

There is an alternate mode of number input via the mouse called 'Active Number Mode' (see below).

To remove all pencil marks from all cells, use the menu option under 'Edit'.

To remove all pencil numbers in a cell, either click the eraser button or simply 'pen' the final choice in.

To remove just one pencilled number in a cell, enter that number again.

You may find this more convenient than toggling between the Pen and Pencil icons.

Holding the Shift key when clicking on a number in the input panel will pencil that number in.

You can undo all the way back to the beginning.

Click the Undo icon (yellow arrow) to undo last input.

Hold Shift key down to enter in pencil (when in Pen mode).

Press the 'P' key to toggle between Pen and Pencil.

Press the space or Delete key to remove any numbers from the highlighted cell.

Use the number keys to enter a number in the highlighted cell.

Use the arrow keys to navigate around the grid.

If you prefer to use the keyboard rather than the mouse, you may:

You can also switch between pen and pencil modes quickly by pressing the 'P' key. To change back to 'Pen' mode, click the 'Pen' icon.You may enter as many pencil marks as you like in each cell.To do this, click the 'Pencil' icon to be placed in 'Pencil mode'.

If you're not 100% sure of a number, you can make a note of it in the cell using the Pencil.Fill in blanks with the Pen (select a cell, then click on the number you want to enter, or enter the number via the keyboard).Move your cursor over the 'New Puzzle' menu item and select a skill level from the dropdown menu.Don't try to solve each of the five grids in turn, you must look at the puzzle as a whole to be able to solve it. Where the grids overlap, the rows and columns do not go beyond their usual length but the interlocking blocks give you more clues. Samurai Sudoku follows the same rules as Sudoku in that every row, column and block of each of the five grids must contain the numbers 1 - 9.

Samurai sudoku rules