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Correct them on the review screen before importing. Every scan stops there first: you see each cell's crop next to what was read and how confident the reader was. Tap any cell to fix it. Green means high confidence, amber medium, red low — so check the amber and red ones first.
For better results, photograph the grid straight on in even light, and fill the frame with the puzzle. Shadows across the grid and steep angles are the usual causes.
That means a digit appears twice in the same row, column, or 3×3 box — usually a misread scan. The offending cells are highlighted in red on the review screen. Fix them and import becomes available again.
No. Digit recognition runs entirely on your device. The app has no networking code at all and works in airplane mode.
No. Your photo is read on your device and discarded once the grid has been extracted. It is never uploaded or stored. See the privacy policy.
Yes — that's what the solver is for. It places one digit at a time and names the technique behind each move in plain English. Press Pause whenever you want to work out the next step yourself, and use undo and redo to step back and forth through the reasoning.
Yes. Every generated puzzle is checked to have exactly one solution, and any puzzle that could only be finished by trial and error is discarded before you ever see it. There is always a logical route through.
Easy through Expert, from a match to a volcano. They differ both in how many cells are blank and in which solving techniques the puzzle actually requires — the harder tiers are harder to think about, not just emptier.
The shield button. With it on, placing a digit that conflicts with its row, column, or box flashes the clash and undoes itself, so you can't build on a mistake without noticing.
Not in this version — starting a new game or importing a scan replaces the current board.
Email pietro.brambilla@icloud.com. Bug reports with a screenshot and the steps that led to it are the most useful.