How to Solve Sudoku: Pointing

Inside a box, the places for a digit lie in a line. Then that digit can be removed from the cells on the same line outside the box.

On Puzzle Lounge it appears from Medium up.

See it step by step

  1. A board full of notes. Look only at the 7s (the small digits are the notes, or candidates)
  2. ● = a cell where 7 can go (notes other than 7 have been removed)
  3. In the left box, 7 has only these 2 places
  4. Both are in row 6 (7 goes somewhere in this row of this box)
  5. The 7 of row 6 is used inside this box (a row holds only one 7)
  6. So the 7s outside the box can be removed (7 goes from row 6, column 5)

This is Hard No.3, partly solved.

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How to find it

  1. Write out your notes (candidates).
  2. Pick a box and see whether any digit's candidates lie in a line inside it.
  3. If so, follow that line outside the box and remove the digit from those cells.

Things to watch

  • All the candidates inside the box must be in the same row (or column).
  • You can only remove it from cells in the same row (or column) outside the box.
Read the full explanation

When a digit's candidates in a box all lie in the same row (or column), the digit goes somewhere in that row of that box. So it can be removed from the cells of the same row outside the box.

Suppose that in a box, 7 can go in only 2 cells, and both are in the same row.

7 must go somewhere in this box, so that row's 7 falls inside this box.

A row holds only one 7. So 7 cannot go in the cells of the same row outside the box.

In the left box, the candidates for 7 are only at row 6, column 1 and row 6, column 3, both in row 6. Row 6's 7 falls inside this box, so 7 can be removed from the candidates at row 6, column 5, outside the box.

Other techniques

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For the basics and how to use notes, see how to solve sudoku, with tips. If you get stuck, the game's hints guide you step by step, starting with where to look.

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