**Welcome to MathDoku!**

MathDoku is a math puzzle similar to Sudoku. Your goal is to correctly fill the entire square field with numbers. Fields come in varying sizes: from 3x3 to 9x9. To fill a cell, select it (using a keyboard or mouse), then select the number. You can type the number from the keyboard or use the panel buttons. A number can be replaced at any time.

**Rows and columns**

Like Sudoku, you can only use each number once per row and once per column. Numbers can be from 1 to the puzzle size (1 to 5 for a 5x5 puzzle). Each puzzle only has one correct solution.

**Segments**

Groups of cells are separated from each other by thick lines. These are segments. Segments of just one cell are there to give you a good start: you can just fill them outright.

**Target numbers 1**

Each segment has a target number in its leftmost upper corner, and an operator next to it: sum (+), deduction (-), division (÷) or multiplication (×). Numbers within the segment, when subjected to that operator, must give exactly the target number.

**Target numbers 2**

4+ means that the numbers’ sum must be 4 (like 3+1), and 2- means that their difference is 2 (like 3-1). 6x means a multiplication producing 6 (like 2x3), and 2÷ means their division gives 2 (like 2÷1).

**Calculator**

Feel free to use the built-in calculator. To turn it on and off, click the calculator button (or use the C hotkey). Click or tap a segment and the calculator will show the result for the filled numbers (left block) and then show how much more must be added (multiplied) for the correct result.

**Notes and Eraser**

To leave notes on which numbers you think can be put into a cell, use the NOTES button (N hotkey). While active, inputting a number will put (or remove, if already there) smaller notes in the cell. Clicking the ERASER button (hotkey Delete or E) clears the cell.

**Reveal and Hint**

If stuck, you can use help. REVEAL option (R hotkey) gives a choice of showing the correct answer for a single cell, the entire segment, or the entire puzzle. HINT button (H hotkey) highlights all the incorrect numbers entered so far. If everything is correct, it will Reveal one of the empty cells instead.

**Difficulty and Puzzle of the Day**

To start a puzzle, you need to choose the size (from 3x3 to 9x9) and difficulty. The higher the difficulty, the larger segments will be, the more difficult calculations are, and the less one-cell segments there will be at the start. Each day, the game also offers three puzzles of the day: these are even harder than Hard, and cannot be Revealed.