The case notes
How a slow thermometer rises
Digits on a slow thermometer never decrease from the bulb; they may stay equal where Sudoku allows it. Watch a worked example, then try the idea in a puzzle.
Put it into practice
A slower rise
This looks like a thermometer, but it is a slow one. Start at the round bulb and move towards the tip.
Rise or stay level
Digits may rise or stay the same. They must never fall. That is the difference from an ordinary thermometer, where every step must rise.
Middle: 4 or 5?
The bulb is four and the tip is five. The middle can only be four or five. But five is already in this same box.
4 → 4 → 5
So the middle is four. Four, four, five is fine here: the matching fours sit in different rows, columns and boxes.
Read the transcript
This looks like a thermometer, but it is a slow one. Start at the round bulb and move towards the tip. Digits may rise or stay the same. They must never fall. That is the difference from an ordinary thermometer, where every step must rise. The bulb is four and the tip is five. The middle can only be four or five. But five is already in this same box. So the middle is four. Four, four, five is fine here: the matching fours sit in different rows, columns and boxes.
