The case notes
How a thermometer rises
Digits strictly increase from the bulb to the tip of each thermometer. Watch a worked example, then try the idea in a puzzle.
Put it into practice
Start at the bulb
This is a nine by nine Sudoku with a thermometer. Read it from the round bulb to the far tip.
Every step rises
Each next digit must be larger. It cannot stay equal, and it cannot fall. The thermometer rises all the way to four.
2 would need a 5
Could the bulb be two? Then the next three cells would need at least three, four and five. But the tip is already four.
1 → 2 → 3 → 4
So the bulb is one. Four increasing cells ending at four have only one order: one, two, three, four.
Read the transcript
This is a nine by nine Sudoku with a thermometer. Read it from the round bulb to the far tip. Each next digit must be larger. It cannot stay equal, and it cannot fall. The thermometer rises all the way to four. Could the bulb be two? Then the next three cells would need at least three, four and five. But the tip is already four. So the bulb is one. Four increasing cells ending at four have only one order: one, two, three, four.
