Click the **Begin** button to get a
puzzle, or enter your own puzzle then click **Begin**.

Skip to step 2 if you want a random puzzle generated for you. If you already have a puzzle and want to enter the clues continue with step 1.

Place the mouse over an empty cell. A number pad will pop up. Click on a digit in the number pad to enter that digit in the cell.

If you make a mistake, click on the cell with the incorrect clue to get a number pad. Then click the correct digit to change the digit in the cell, or click on the currently selected digit to clear the cell.

You will not be allowed to enter duplicate digits in any row, column or block. When you attempt to make an illegal entry the the prior instance(s) of the digit will be highlighted.

**Clear:**- All the numbers on the board are cleared, except the clues.
**Reset:**- Start a new puzzle, all the numbers on the board are cleared, including the clues.

**Auto-fill:**- Markup digits are supplied for each cell by eliminating digits which are already present in the cell’s row, column and block.
**Clear:**- All markup digits are cleared.

When all the clues have been entered, click the **Begin**
button. Or if you skipped step 1 and didn’t enter any
clues, clicking the **Begin** button creates a puzzle for
you.

You may now start solving the puzzle. Digits are entered in the empty cells via the number pad, as before but with a new feature. Holding down the shift key while clicking a digit in the number pad enters it as a markup digit (a small red digit). This is a way to keep track of which digits could potentially be placed in that cell. If a markup digit is already set, shift-click will clear the markup digit.

**Save:**- Saves the current state of the board so you can return to it later. Checkpoints do not persist when you leave the page, in other words, you cannot save a checkpoint, turn off your computer or close your browser and return to the same puzzle later because the checkpoint is lost when you exit the page. More than 1 checkpoint may be saved.
**Restore:**- Return to the most recently saved checkpoint, or more accurately, return to the most recently saved checkpoint that has not already been restored.

If you don’t wish to solve it yourself, or tried but
couldn’t solve it, click on the **Solve it** button
to display the solution.

**Show Errors:**-
This only warns you if you try to enter a digit that is already
in another cell of the row, column or block where you are
entering the digit. This option
warn you of all incorrect solutions!*does not* **Show Digits:**- This option will highlight all cells with a particular markup digit or digits.

**Difficulty score:**- A number that estimates the puzzle’s difficulty.
**Technique Level:**- The level of the most advanced solution technique required. This corresponds to the difficulty (Easy, Medium, Hard or Expert) of puzzles published at the Iron Sudoku web site.
**Time:**- Keeps track of how long it takes you to solve the puzzle.