Technique

Pointing Pairs

When a digit inside one box only fits in cells that share a row or column, it can be crossed off the rest of that row or column outside the box - the box itself is 'pointing' the digit into a line.

💡 What It Is

A box-to-line elimination. If every remaining candidate cell for a digit within one box lies on the same row or column, the digit is locked into that line as far as the box is concerned.

🔍 How To Spot It

Pick a box and a digit. List every empty cell in the box that could still hold it. If they all sit in one row or one column, you have a pointing pair (or triple).

✅ Why It Works

The digit has to go somewhere in the box, and every legal spot for it sits on the same line - so that line's cells outside the box can't be it.

📝 Worked Example

In box 1, the digit 4 is only a candidate at R1C2 and R1C3 - both in row 1. Since 4 must land in box 1 and both its spots are in row 1, eliminate 4 from every other cell in row 1 (R1C4 through R1C9).

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