Fill the white cells with digits from 1 to 9 so that each run of cells — across or down — adds up to the number at its head.

A clue cell is cut by a diagonal: the number above it is the sum of the cells to its right, the number below it the sum of the cells beneath.

Within one run no digit appears twice.

Tap a white cell and pick a digit on the pad under the board; the same digit again clears it. With notes on, digits are pencilled small in the cell instead.

A reddish cell holds a digit its run already has, or sits in a run whose sum has gone wrong; a sum greys out once its run is done.

Learn the solving techniques