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The Pointing Pair strategy applies when a specific candidate within a 3×3 box can appear in only two cells that lie in the same row or column.
This is the basic form of the Pointing technique. This time, we only need two cells pointing to the same row or column.
Look at the middle 3×3 box. Let's analyze the positions of candidate 7 within it.
Candidate 7 is already impossible in the other cells of this box. We therefore have exactly two possible positions for 7 - both in Row 5.
This is the key piece of information. Since all possible positions for 7 in this box are located in Row 5, the 7 must go into one of these two cells.
This means that the remaining cells in Row 5 outside this box cannot contain 7.
Since candidate 7 is now confined to the middle box, we can remove it from the remaining cells in Row 5.
This is the essence of Pointing Pair: when all possible occurrences of a digit within a box point to one row, we can remove that digit from the rest of that row outside the box.
