Platon Sudoku · Sudoku Study

Sudoku pencil marks: how to use candidates

A candidate is a digit that may still fit in an empty cell. It is a possibility, not a placed answer. How to Play.

This course is adapted from Platon Sudoku App. Read the complete example here, then continue learning and practising in the app.

What to look for

A candidate is a digit that may still fit in an empty cell. It is a possibility, not a placed answer.

Check that the cell is empty, then rule out digits already placed in its row, column and box.

A small note is a candidate; a large placed digit is not. The local diagram shows only relevant notes.

Look at the highlighted row, column and box. Both 3 and 7 are still possible here; we cannot decide yet.

Our puzzles have one complete solution, but a candidate is not an answer. Note 3 and 7, then look elsewhere.

In this new cell, the digits already in its row, column and box rule out every possibility except 7.

Once 7 is filled, the original cell can no longer contain 7. Only 3 remains.

Solve a cell you can justify, then return to the uncertain ones. Each confirmed digit can reveal a new clue.

Read the related lesson, inspect its example, then return to your puzzle.

This course is adapted from Platon Sudoku App. Read the complete example here, then continue learning and practising in the app.