The case notes
How a diagonal sum clue works
A clue outside the grid gives the sum along its indicated diagonal. Digits may repeat if ordinary Sudoku rules allow. Watch a worked example, then try the idea in a puzzle.
Put it into practice
Outside clue. Diagonal sum.
A diagonal sum clue sits outside the grid. Follow its arrow across the diagonal, and add every digit it touches.
1 + 5 + 9 = 15
This clue is twenty. The first three cells give us one, five and nine. Together they make fifteen.
20 − 15 = 5
Twenty minus fifteen leaves five for the last cell. Notice that there is already a five on this diagonal. That is allowed here.
Repeats can be allowed
A diagonal sum diagonal is a sum, not a no-repeat cage. These fives are in different rows, columns and boxes, so both can stay.
Read the transcript
A diagonal sum clue sits outside the grid. Follow its arrow across the diagonal, and add every digit it touches. This clue is twenty. The first three cells give us one, five and nine. Together they make fifteen. Twenty minus fifteen leaves five for the last cell. Notice that there is already a five on this diagonal. That is allowed here. A diagonal sum diagonal is a sum, not a no-repeat cage. These fives are in different rows, columns and boxes, so both can stay.
