How to Use Notes (Pencil Marks) in Sudoku

We filled in notes for most of this board. Every dot marks a color that could still go in that cell, based on the bubbles already placed. Three cells down the middle of the center block are still empty. Help us finish them.

Write a note only when you can prove it, never when you are guessing. A Turquoise bubble sits in this row, just outside the block, so the middle cell cannot be Turquoise. Turquoise can still go in the other two cells, so each one gets a Turquoise dot.

You do not have to note everything at once. The easiest stage is following one color through one block. A Dark Green bubble sits in this row too, so the middle cell cannot be Dark Green. Dark Green joins Turquoise in the other two cells. This stage is quick and keeps the board easy to read. So far you have narrowed two cells, but no cell has an answer yet.

The next stage looks at one cell and asks what can still go there. This block is missing Orange, Dark Green, and Turquoise. The middle cell shares its row with Dark Green and Turquoise, so Orange is the only color that fits. Give it an Orange dot.

When a cell has only one dot left, you have found its answer. Place Orange. After you place a bubble, remove its color from the notes in the same row, column, and block. Watch the three Orange dots disappear as the bubble lands.

Removing those dots just solved another cell. Look two cells below. That cell had two dots, Orange and Dark Purple. The Orange dot is gone now, so only Dark Purple is left. Place it, and remove its notes too. One answer often leads to the next.