Choose a digit that already appears a few times on the grid.
Scanning (Cross-Hatching)
The first technique every solver learns, and the one you will use most.
Scanning, also called cross-hatching, is how you place digits without any pencil marks at all. You pick one digit and ask, box by box, where it is still allowed — letting existing copies of that digit in rows and columns rule out cells.
Worked example
5
1
3
8
1
1
1
How to apply it
Pick a box that does not yet contain it.
Mentally draw lines through every row and column in that box that already hold the digit — those cells are blocked.
If exactly one empty, unblocked cell remains, the digit must go there.
Repeat for each box, then move to the next digit.
When to use it
Scanning is your opening move on every puzzle and the technique you return to after each placement. On easy and many medium grids it is almost all you need.
Frequently asked questions
What is the difference between scanning and cross-hatching?
They are the same technique — cross-hatching just describes scanning a box from both its rows and its columns at once.