Note a digit in a box only when that box has exactly one or two cells where the digit can still go.
Three or more possible cells: skip the box and return to it later.
Applying it, step by step
Select a digit — start with 1. Then, for every box on the board:
- If the box already contains the digit, skip it. It’s resolved for this digit.
- List the box’s empty cells.
- Cross out every cell whose row already contains the digit anywhere on the board.
- Cross out every cell whose column already contains it.
- Count what remains. One cell: note it — you know exactly where the digit goes in this box. Two cells: note both — the digit is in one of them. Three or more: write nothing, move on.
Repeat for every box, then for every digit up to 9 (6 in a Mini). That’s one Notation Pass.
Why not note everything?
Imagine digit 4 could go in four cells of a box. Writing all four records a fact, but a useless one: you can’t conclude anything from it, and nothing elsewhere gets narrower. Worse, when later information eliminates two of those cells, you have to go back and erase them, and erasing the wrong one is exactly how solves go off the rails.
Wait until the box is down to two, and the notes you write are immediately meaningful. They constrain their rows and columns, they pair up with other notes, and they’re one step from resolution.
There’s a second benefit. A board that holds only one- and two-cell notes is a board that is close to solved: every digit in every box is either placed, pinned to one cell, or pinned to one of two. That’s the level of precision the Final Pass needs.
What it looks like on a real board
This is a real beginner puzzle from the NOTE-KU Starter Pack, after a single pass with the rule. Every small number is a digit that had only one or two possible cells in its box. Empty cells sit in boxes where digits still had three or more options — they get their notes on a later pass, once eliminations narrow them down.
A worked example
ML has six empty cells. Two sit in rows that already contain a 3; one sits in a column that already contains a 3. Three are eliminated, three remain — so ML is skipped for digit 3.
Two passes later, a 3 is settled in a box that shares a row with one of those three cells. Now only two remain. Return to ML and note the 3 in both.
When is a digit “done for now”?
A digit is exhausted for this pass when every box either holds it, has one or two notes for it, or was skipped because three or more cells are still open. In the NOTE-KU app, a ✓ NOTED badge appears on the digit at that moment. It’s your cue to move on and come back after other digits have done their work.
Common mistakes
- Counting only givens in the box. Constraints come from the whole row and column, across the board.
- Forgetting to come back. Skipped boxes are a to-do list, not a dead end.
- Writing three “just in case”. Resist it. If it’s three, it isn’t information yet.
Practice it now.
Every puzzle in the app has exactly one solution and can be solved by logic alone.
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