Last Digit
When eight copies of a digit are on the board, the ninth has one place left.
What it is
Pick one digit, not one cell. When you can see it eight times, only one copy is missing. Its row, column and box meet in one empty square, so the ninth copy goes there. That square may still allow other numbers locally; counting the digit makes the move certain.
How to spot it
After a move, glance at the digit counts. Does a digit appear eight times? Follow the missing row, column and box to their one shared square. You are simply finding the ninth copy.
Worked example
One question at a time: count the 1s, then find the missing ninth place.
Step 1 of 4: Look at the marked square
This square may allow more than one number. We will prove one number from the whole board.
Why it matters
Last Digit gives beginners a quick whole-board routine: notice a nearly complete number and finish its set of nine.
Practise now
Solve a puzzle where this technique decides the game
Frequently asked questions
How is this different from a Hidden Single?
A Hidden Single looks inside one row, column or box. Last Digit looks at all nine copies on the board. The final placement can qualify as both, but counting is often easier to see.
Do I need pencil marks for Last Digit?
No. Look only at the large placed digits. Once you see eight copies, follow where the ninth is missing.
Put it to use
Where you will meet it
This pattern is the backbone of easy grids. Start one and you will use it within a few moves.
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