Pointing Pairs vs Box-Line Reduction: Key Differences

Pointing Pairs and Box-Line Reduction are both types of locked candidate techniques, but they differ in direction. A Pointing Pair pattern allows you to use candidates confined to a single row or column within a 3x3 box to eliminate those same candidates from the rest of that row or column. Box-Line Reduction does the opposite: it uses candidates confined to a single box on a row or column to eliminate them from the rest of that box. Understanding this directional difference is key to applying them correctly and solving more puzzles efficiently.

By SudokuHint TeamLast updated June 21, 2026

What is a Pointing Pair?

A Pointing Pair, sometimes called a Pointing Triple, occurs when a candidate digit appears only in one row or column within a specific 3x3 box. Because all instances of that digit in the box are aligned, you know the digit must be placed somewhere in that line segment. This logic lets you eliminate that candidate from all other cells in the same row or column that lie outside the box. It's a powerful way to use box constraints to clean up a line. You can learn more about the specifics of this pattern on our dedicated Pointing Pairs technique page.

For example, if in a given box, the candidate '5' only appears in two cells, and both are in the top row of that box, you have a Pointing Pair for '5'. You can then safely remove '5' as a candidate from all other cells in that top row that are in the other two boxes.

Look for a candidate that appears 2 or 3 times in a box, but only in one row or one column.
The elimination happens along the entire row or column, but only in the cells outside the box you found it in.

Key insight: Think: The box 'points' to where the digit must go on the line, allowing you to clean up the rest of that line.

What is Box-Line Reduction?

Box-Line Reduction, also known as Locked Candidates Type 2 or Claiming, is the mirror image of a Pointing Pair. This pattern is found when a candidate digit is confined to a single 3x3 box within a specific row or column. Because the digit for that entire row or column must be placed inside that one box, you can eliminate it as a candidate from all other cells within that same box. Our Box-Line Reduction guide offers a deeper dive with examples.

Imagine you are scanning a row. If the candidate '3' only appears in three cells of that row, and all three of those cells happen to be in the same 3x3 box, you have found a Box-Line Reduction. You can then erase '3' from every other cell in that box.

Scan each row and column. If a candidate appears only in cells that all fall within one box, you have a Box-Line Reduction.
The elimination happens inside the box, removing the candidate from cells not on the initiating row or column.

Key insight: Think: The row or column 'claims' the candidate for a specific box, allowing you to clean up the rest of that box.

Side-by-Side Comparison: Key Differences

The core difference is the direction of logic and the resulting elimination scope. Both are locked candidates sudoku strategies, but they start from different points. A Pointing Pair starts its logic within a box. You look inside a single 3x3 box, notice a candidate is restricted to one line (row/column), and then eliminate along that full line outside the box. Box-Line Reduction starts its logic on a line. You look along an entire row or column, notice a candidate is restricted to one box, and then eliminate inside that box.

This table summarizes the critical distinctions:

In practice, you will often use these techniques in tandem. Solving a Pointing Pairs and Triples pattern might reveal a Box-Line Reduction, and vice versa. Mastering both significantly increases your solving speed on intermediate puzzles.

Key Facts

▪Pointing Pairs and Box-Line Reduction are the two subtypes of the locked candidates solving technique.
▪A Pointing Pair pattern is identified when a candidate appears only in one row or column within a specific 3x3 box.
▪Box-Line Reduction is identified when a candidate appears only in one 3x3 box within a specific row or column.
▪For a Pointing Pair, you eliminate the candidate from the rest of the row or column outside the box where it was found.
▪For Box-Line Reduction, you eliminate the candidate from the rest of the box outside the row or column where it was found.
▪Pointing Pairs are also called Locked Candidates Type 1, while Box-Line Reduction is Locked Candidates Type 2 or Claiming.
▪Both techniques rely on the basic Sudoku rule that a digit must appear exactly once in every row, column, and box.
▪These are intermediate techniques often used after basic methods like sole candidates and hidden singles.

Frequently Asked Questions

Can a pattern be both a Pointing Pair and Box-Line Reduction?

Yes, though it's rare. If a candidate in a box is confined to one row, and that same candidate in the row is confined to that one box, the pattern satisfies both definitions. The eliminations from both techniques would apply.

Which technique should I look for first?

There's no strict order. Many solvers scan boxes for Pointing Pairs and rows/columns for Box-Line Reduction simultaneously. Our hint engine often suggests the one that creates the most immediate eliminations in the current puzzle state.

Are Pointing Triples treated the same as Pairs?

Yes. The logic is identical whether the candidate appears in two cells (a pair) or three cells (a triple) within the aligned line of the box. The elimination rule does not change.

How do these relate to Hidden Pairs/Triples?

They are different. Hidden Pairs/Triples involve two or three candidates hidden among others in a unit. Locked candidates (Pointing/Box-Line) involve a single candidate's position being restricted, forcing eliminations in a connected unit.