Scanning
Follow one digit into a box: the lines that already contain it cross out every other square.
What it is
Pick one digit and look in a box where it is missing. Every placed copy keeps that digit out of the rest of its row and column. Imagine those visible lines entering the box. If they cross out all but one empty square, the digit belongs in the square left over. That square may still allow other digits — this is why scanning is different from a Naked Single.
How to spot it
Start with a digit you can already see several times. Find a box where it is missing, then check the three rows and three columns through that box. A row or column already holding the digit crosses out its square in the box. Do not count pencil marks: just follow the visible digit until one square remains.
Worked example
One question per step: follow the 9 into the highlighted box.
Step 1 of 4: Look at the highlighted box
The 9 is still missing here. It must go somewhere in this box.
Why it matters
Scanning is the quickest way to find many moves in easy and medium Sudoku. It builds the habit behind later techniques: look for what is visibly impossible before reaching for notes.
Practise now
Solve a puzzle where this technique decides the game
Frequently asked questions
Do I need to write anything down when scanning?
No. Scanning is deliberately a mental technique. Notes become useful when scanning stops producing placements, typically on hard puzzles.
Which digit should I scan first?
The one that appears most often. Six or seven copies of a digit create many blocking lines, so the remaining cells are heavily constrained.
Put it to use
Where you will meet it
This pattern is the backbone of easy grids. Start one and you will use it within a few moves.
Play EasyStuck on a grid of your own?
Type the position into the solver and it walks the whole solution, naming the technique behind every step — including this one.
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