How to Use Notes (Pencil Marks) in Sudoku

Most of this board already has notes. Each dot is a color that could still go in that cell. Three cells in the center of the board are still empty. Fill in their notes next.

Only add a note when you are sure the color can go there. A Turquoise bubble sits in the middle cell’s row, just outside the block, so the middle cell cannot be Turquoise. The other two cells can, so each gets a Turquoise dot.

You do not have to note everything at once. Note in stages, starting with one color in one block. This keeps the board easy to read. A Dark Green bubble also sits in the middle cell’s row, so the middle cell cannot be Dark Green. The other two cells get a Dark Green dot.

Now look at one cell and ask what can go there. This block is missing Orange, Dark Green, and Turquoise. The middle cell cannot be Dark Green or Turquoise, so it gets an Orange dot.

A cell with only one dot is solved. Place Orange. Then remove Orange from the notes in the same row, column, and block. Three Orange dots disappear.

Look two cells below. That cell had Orange and Dark Purple. The Orange dot is gone, so only Dark Purple is left. Place it. One answer often leads to the next.