How to Use the Pointing Pairs Strategy in Sudoku

As you move deeper into intermediate Sudoku puzzles, you will need strategies that look at how different regions of the board interact with one another. The Pointing Pairs technique (sometimes involving three cells, known as Pointing Triples) is a fantastic tool that uses the layout of a single 3×3 block to eliminate candidates across an entire row or column.

Pointing applies when a candidate appears only in one row or column within a box. When this happens, that box “points” down the line, clearing out impossible numbers.

The Logic Behind Pointing Pairs

Every 3×3 block must contain the numbers 1 through 9. Sometimes, when you fill out your pencil notes, you will notice that a specific number is completely restricted to just one line inside that block.

Let’s look at this box. All cells that might contain the value 4 are located in the same column.

Because the number 4 must be placed somewhere inside this box, and the only available spaces for it sit on that specific vertical line, we hit a logical certainty: 4 must definitely be placed in one of these two cells.

The Power of Elimination (Step-by-Step)

Once you establish that the number 4 is locked into that column inside the box, it has massive consequences for the rest of that line:

1. Find the restriction: Scan a 3×3 block and notice that a candidate (like 4) only appears in a single row or column within that block.
2. Project the line: Extend your eyes along that entire row or column across the whole 9×9 grid.
3. Clear the outside cells: This means that 4 can’t appear anywhere in the column outside the box.

Because that specific block is guaranteed to claim the number 4 on that line, no other cell in that column (in the blocks above or below it) can possibly hold a 4. You can safely delete the number 4 from the pencil notes of every other cell along that entire line outside of your target box.

Pointing Rows vs. Pointing Columns

This strategy is highly versatile and works in both directions across the grid:

• Pointing Columns: As shown in our example, a vertical alignment inside a box eliminates candidates in the rest of the column above and below the box.
• Pointing Rows: If all candidates for a number inside a box are lined up horizontally, they form a pointing row. You can instantly erase that candidate from all other cells to the left and right of that box along the same row.

Speed Up Your Grid Clearing

Mastering Pointing Pairs is a crucial step in advanced scanning. It allows you to make deductions about rows and columns without even knowing the final answer for the cells you are looking at. Cleaning up these outside lines is often the secret key to unlocking Naked Singles elsewhere on the board.

Ready to point out the answers? Test your scanning skills right now on our Hard Sudoku Puzzles or Expert Sudoku Puzzles, activate your notes, and look for those aligned candidates!