Pointing pairs: let the box point down a line

A pointing pair or triple appears when every candidate for one digit inside a 3×3 box lies on the same row or column.

Key idea

The box must place the digit on that line, so the same digit is impossible on the rest of the line outside the box.

See the move, step by step

Follow candidate 6 from box 1 into row 1.

Step 1 of 4

In box 1, look only at candidate 6 and keep row 1 visible beyond the box.

Box and line being checked

Step 2 of 4

The only 6s in box 1 are R1C1 and R1C2. One of them must supply the box's 6.

Box and rowCandidates locked to row 1

Step 3 of 4

R1C7 lies on the same row but outside box 1, so it cannot also contain 6.

Locked candidatesCandidate to remove

Step 4 of 4

The pair remains unresolved, but R1C7 is cleaner and may now combine with another deduction.

Pointing pairUpdated cell

Filter for one digit and scan each box. Whenever all its candidates align, follow that row or column outside the box.