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Module 4 · IntermediateLesson 13 of 28

Pointing Pairs

Find a digit confined to one row or column inside a box and eliminate that digit from the line outside the box.

Outcome

You can start inside a box, recognize when every candidate for one digit lies on the same row or column, and eliminate that digit from the line outside the box.

Intro copy

Pointing has one reliable starting question:

Inside this box, does digit X live on one line?

If yes, the box can eliminate X farther along that line.

Step 1 — Build the rule visually

Start with one empty 3×3 box plus its crossing row.

Place two candidate 5s inside the box on the same row.

Prompt:

The box still needs a 5. Where must that 5 appear?

Learner selects the shared row.

Then reveal candidate 5s outside the box.

Prompt:

Which of these can survive?

Learner removes them.

Final label:

Box → line = Pointing

Step 2 — Guided row example

Required state: Digit 8 appears in exactly two source cells in one box, both on the same row.

Prompt sequence:

  1. select all source 8s;
  2. select their shared line;
  3. remove outside 8s.

Correct feedback:

Good. You still do not know which source cell is 8, but you know the row receives its 8 inside this box.

Step 3 — Column example

Same interaction, rotated vertically.

Prompt:

Do not search for a row this time. What do all source candidates share?

Correct: column.

Step 4 — Pointing Triple

Show three candidate 4s in one box, all on one row.

Prompt:

Is the box still pointing?

Correct: Yes.

Microcopy:

Count is not the rule. Alignment is.

Step 5 — Near miss

Show:

  • two candidate 9s on one row;
  • a third candidate 9 elsewhere in the box.

Prompt:

Can the box eliminate 9 along the first row?

Correct: No.

Feedback:

The box has another possible 9 outside that row, so the restriction is incomplete.

Practice

Mix:

  • row and column Pointing;
  • two- and three-source forms;
  • productive and non-productive alignments;
  • near-misses.

Hint ladder

  1. Digit: “Focus on candidate 7.”
  2. Unit: “Inspect this box.”
  3. Relationship: “Do all candidate 7s share one line?”
  4. Direction: “The box points along a row.”
  5. Reveal: Highlight valid outside eliminations.

Completion

Four correct Pointing eliminations plus two near-miss classifications.

Next

Box-Line Reduction

The geometry is similar, but the source flips from box → line to line → box.

Reference

Read Pointing Pairs for the Pair/Triple terminology and connection with Crosshatching.