Next steps

Locked Candidates: pointing versus claiming

These techniques use the overlap between a box and a row or column. Their starting conditions point in opposite directions, so be clear about which unit you checked.

Practise on a board ↓

Compiled by Sudoku-Y · Updated 2026-10-12 · Our research and editorial process

Locked Candidates · Pointing / Claiming

Try removing the 6s yourself

These two moves look alike, but start in different places. Try each one, then change a condition and see what breaks.

This is our own partial teaching board. Every small digit is a candidate, not a placed value. Your saved game stays untouched.

The top-left box has just two spots for 6: B1 and B3. Tap the 6s you can remove from row B.

We checked the whole box: no placed 6, and only these two spots allow 6. Dots elsewhere do not mean that other digits are ruled out.

Green outline = evidence when shown · Crossed out = a candidate you removed

Tap a candidate 6 you think can go

Change the condition: Try adding 6 at C2

See why

1. Box → row

Put 6 at either B1 or B3: row B gets its 6 inside this box. So B5 and B8 cannot be 6. We still cannot choose between B1 and B3.

Now C2 can be 6, the box could use row C instead. The old reason no longer lets us remove 6 from B5 or B8.

2. Row → box

Row B needs its 6 at B1 or B3, both in the same box. That box must use its 6 in row B, so A2 and C3 cannot be 6. B1 versus B3 is still undecided.

With B5 available, row B could put its 6 outside the top-left box. The old reason no longer rules out 6 at A2 or C3.

Try it on your own game

First check that the unit has no placed 6, then check every possible spot. Incomplete pencil notes are not proof. On Classic 9×9, tap Techniques to look for a move on your own board.

LOOK · TRY · UNDERSTAND

Try it and see why

Pick something to practise

An elimination is still progress

The empty cells in row D have the complete notes shown. Large digits are already placed.

Our own partial teaching board, not a full puzzle. Large digits are placed values; small digits are candidates. Dots mean the cell is not described here. Complete candidate lists are part of the stated scenario, not calculated from the dots.

Green outline = evidence · Purple “try” = an assumption · Crossed out = removed candidate

Use the D1/D4 pair to remove candidates from D7. What remains?

Select a cell, then tap a candidate below.

Choose a cell on the board

Removed 0/2

See the reasoning

After removing 2, 8, D7 still allows 5, 6. Do not enter 5 yet: D7/D9 can still swap those digits. The elimination is useful progress.

Digit set 1/9 · A different digit set in the same pattern, not a new full puzzle.

Read the source principles: HoDoKu — Naked Subsets

Pointing starts inside a box

When every position for a missing digit in a box lies on one row, that box must place the digit on that row. Eliminate it from the same row outside the box. Columns work in the same way.

HoDoKu — Intersections · SudokuWiki — Intersection Removal

B1 · B36 ?Only 6s in box 1

B5 · B86Same row, outside box 1

Original teaching scenario. Only the stated conditions are shown; this is not a complete Sudoku puzzle.

Example with digit 6

Suppose the top-left box needs 6 and its only positions for 6 are B1 and B3. Remove 6 from B5 and B8: they share row B but lie outside that box.

Try before revealing

What if C2 in the same box also allows 6?

Show explanation

Then pointing along row B is not established. The box could place 6 in C2. You must inspect every candidate position in the box.

Claiming starts with a row or column

Reverse the direction. If the only positions for 6 in row B are B1 and B3, that row must use 6 in their shared box. Eliminate 6 from the other cells of that box outside row B.