Getting started — click an empty cell, then pick a number from the pad or your keyboard. The pre-filled numbers are givens and can't be changed.

Mistakes — a wrong digit is flagged right away. Three mistakes and it's game over, so double-check before you commit.

Not sure yet? — toggle Notes to jot down candidate numbers in a cell instead of committing to one - handy for narrowing down the possibilities before you decide.

Stuck? — Hint fills in one correct cell for you (3 per puzzle), and Undo takes back your last move.

Difficulty — switch tabs above the board - fewer starting clues means a harder puzzle.