Notes: pencil marks for when you are stuck
Updated
The grid goes quiet, and the empty cells still have several digits each. You can write those digits down. A note says “this is still legal here.” It does not say “this is the one.” I once treated a pencilled 7 as a decision. It was only a possibility. The next pair was much less forgiving.
When to write them
Scan for naked singles and hidden singles first. If empty cells remain, write the candidates, or leave the grid bare and keep looking. The choice is yours. Notes are not a rung on the ladder. Turning them on does not make a puzzle Easy, Medium, Hard, or Expert.
This example is a place where the usual ladder does not place or delete anything yet. Row 1 is filled through column 6. The three open cells, r1c7, r1c8, and r1c9, each allow 7, 8, and 9. None of those cells is a single, and none of those digits has a single home in the row. The lists are worth keeping. They are not worth filling.
Where to look
In an empty cell, write every digit that is still missing from its row, column, and box. These three cells see 1, 2, 3, 4, 5, and 6 along row 1. Their box and columns add nothing further, so the lists are 7, 8, and 9.
The top-left and top-middle boxes are filled. We only need the three open cells in row 1 for this example.
The step
- Finish the singles you can see, or decide you cannot see any.
- For an empty cell, cross off digits already in its row, column, and box.
- Write what remains. One digit left is a naked single. Place it. Do not leave it as a note.
- When you later place a digit, erase it from the notes in the same row, the same column, and the same box.
Suppose you place 7 in r1c7. The 7 notes in r1c8 and r1c9 have to go, because they share the row. The cell you filled loses its list entirely. It is an answer now. A leftover 7 in a neighbor is how a later pair goes wrong. The pair will treat that 7 as still legal.
Written by hand, or listed for you
Pencil marks are yours to write. An automatic candidate list is a different tool. The current play screen provides manual Notes, off by default. It records the digits you choose. The example below comes with its marks already prepared, and you can show or hide them. A handwritten list is easier to leave incomplete, and a hole in the list will lie to you when you look for pairs.
The marks stay candidates. They are not a second solution, and they do not change the grade. The grade was fixed when the puzzle was built, from the hardest step it needs. That table is on the difficulty page.
Example
The three open cells each allow 7, 8, and 9. The marks can be shown or hidden. None of them is an answer yet.
You can show or hide the marks. Hiding them does not change the grid. It only changes whether you are looking at the lists.
Easy to misread
A note is not a small answer. Two cells that both say 7 and 8 still have not told you which one is 7. Treating the first mark you like as the digit will break the pairs on the next page.
Do not keep a list from memory after the grid has changed. Every placement deletes notes. Skip the deletion, and the old 7 sits in a cell that can no longer hold it.
Skipping notes is allowed. Some grids stay readable without them. With or without marks, it is still the same puzzle, with the same grade.
Next
When the lists feel trustworthy, pairs start to show. Next time you are stuck with three digits and no single, try the page on pairs.