What a note actually says
A note is a small digit written inside an empty cell. It means one precise thing: given everything I can currently see, this digit has not been ruled out here. It isn’t a hunch or a guess; it’s a statement of evidence. That’s why accuracy matters so much. A correct note adds information to the board. A wrong one — a digit that was already ruled out by something you missed — adds noise that will eventually produce a wrong answer.
How most players use notes
Most of us use notes reactively. We hit a cell we can’t solve, pencil in whatever seems plausible, and move on. Three problems follow:
- They’re incomplete. Some cells have notes, some don’t; some digits were checked, others weren’t.
- They go stale. A number placed elsewhere rules a note out, but nobody goes back to erase it.
- They can’t be trusted. And notes you can’t trust are worse than none, because you make decisions from them.
Full candidates vs. selective notes
One common answer is “full candidate mode”: write every possible digit in every empty cell, then erase. Many apps even offer a button that fills them all in. It’s complete, but on a fresh board it buries you in information that says almost nothing — a cell with six candidates tells you very little — and every one of those candidates has to be maintained by hand.
Other apps split notes into “corner” and “centre” marks, a convention from competitive solving. It works, but it’s another system to learn.
NOTE-KU takes a third path: selective notation. You scan one digit at a time and write it only where it’s down to one or two cells in a box. The board starts sparse and gets more precise with every pass, instead of starting cluttered and getting cleaner.
| Approach | On a fresh board | Main risk |
|---|---|---|
| Reactive notes | Few, scattered notes | Gaps and stale notes |
| Full candidates | Every cell full of digits | Overload; missed erasures |
| NOTE-KU (selective) | Only 1–2-cell digits noted | Skipped boxes must be revisited |
Notes as the method
The real shift is in intent. A conventional solver uses notes as a memory aid. A NOTE-KU solver uses notes as the method itself: no answer is written until the notation has proven it, and when every empty cell holds exactly one candidate, the whole board is confirmed in a single Final Pass.
In the NOTE-KU app each cell holds up to three notes, which is plenty when you follow the Two-Candidate Rule, and the digit you select is highlighted everywhere on the board — in cells and in notes — so you can read a digit’s whole situation at a glance.
Three habits for notes you can trust
- Scan by digit. Finish one digit across all boxes before starting the next.
- Write only what’s narrow. One or two cells in a box: note. Three or more: wait.
- Erase immediately. When something rules a note out, remove it on the spot, and look for what that removal unlocks.
Practice it now.
Every puzzle in the app has exactly one solution and can be solved by logic alone.
More guides
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Read ▸The Two-Candidate Rule: When to Write a Sudoku Note
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Read ▸Stuck on a Sudoku? Test, Don’t Guess — Temp Mode
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