Pointing
A box confines a candidate to one row or column.
Explanation
If all possible cells for a digit inside a box sit on the same row or column, that digit must be placed there. Remove it from the rest of that row or column outside the box.
Practice tip
Use candidate notes; scan each box digit by digit for candidates lining up.
Example steps
- Find a box where one candidate only appears on a single row or column.
- That line must host the digit inside this box.
- Remove the candidate from the same line outside the box.