Outcome
You can choose a useful scanning target and use the solved grid to find a forced placement.
Intro copy
Do not scan the whole board with no plan.
Give your eyes one target: a nearly complete unit, one digit, or one promising cell.
Step 1 — Explain
Show a puzzle with several unsolved areas.
Copy:
A good scan has a target. Start with a row, column, or box that is nearly complete — or choose one digit and track where it can still go.
Step 2 — Guided example
Required state: One row with two empty cells and crossing constraints that force one missing digit.
Prompt
This row is missing two digits. Which empty cell should we inspect first?
Hint 1
Check the columns crossing the two empty cells.
Hint 2
One missing digit is already present in one of those columns.
Correct feedback
Good. One crossing column removes the ambiguity, so the other cell is forced. That is the value of a focused scan.
Incorrect feedback
That choice is not forced yet. Compare the columns crossing both empty cells and look for the missing digit one column already blocks.
Step 3 — Try it
Exercise spec
Present a box missing one target digit. Existing copies in crossing rows/columns leave one valid position. Do not pre-highlight the blockers.
Prompt:
Find where 7 must go in this box.
Correct feedback
Correct. Every other cell in the box is blocked by a row or column containing 7.
Incorrect feedback
Check the rows and columns that already contain 7 before choosing a cell.
Step 4 — Practice
Three controlled states:
- nearly complete row;
- digit scan in a box;
- nearly complete column.
Checkpoint
Present a mixed puzzle state with no scan type label.
Prompt:
Find one forced placement using only the solved digits already on the board.
No candidate overlay until the learner requests a hint.
Completion
- three guided scan tasks correct;
- checkpoint solved without a wrong placement;
- hints allowed but recorded for progression analytics.
Next
Crosshatching — learn a focused one-digit scan that uses crossing rows and columns inside a box.
Reference
Read the full Scanning in Sudoku Guide for the complete scanning workflow.