Rules and the board

The rules

1. Each run of white cells adds up to the clue in the black cell at its start.
2. Only the digits 1 to 9 are used.
3. A digit never repeats in a run.

The board

A black cell shows two clue sums, split diagonally. The number in the top right is the Across run to its right. The number in the bottom left is the Down run below it. A black cell with only one number has only one run.

A white cell shows a large digit when it is placed. The small digits in the corner are pencil marks.

The digit pad

Tap a cell, then tap a digit. Tap the same digit again to clear the cell. The number under each digit counts how many of that digit are still unplaced in the puzzle.

Pencil marks

Turn on Notes and the digit pad writes small pencil marks instead of digits. With "Keep the pencil marks up to date" in the settings, the app fills the marks from the digits the solver still allows, and leaves the cells you have edited by hand alone.

Undo, redo and erase

The board tools under the puzzle undo and redo a move, wipe every pencil mark, open the solve path and start a "Why not?" proof.

Next: Your first puzzle.