Kakuro combinations
The totals that can only be made one way, and how to use them.
Some totals have just one set of digits. Two cells: 3 = 1+2, 4 = 1+3, 16 = 7+9, 17 = 8+9. Three cells: 6 = 1+2+3, 7 = 1+2+4, 23 = 6+8+9, 24 = 7+8+9. Four cells: 10 = 1+2+3+4, 30 = 6+7+8+9.
When a run has a unique combination, you know which digits it uses. Where it crosses another run, the shared cell must use a digit common to both.
On harder grids, list two or three combinations per run and eliminate them by crossings.
Practise it
The Hint button on every puzzle explains the next step in the same plain language, so you can learn as you play. Play a Kakuro puzzle.