Box Brain Sudoku
Learn › Thermometer Bounds
Easy · technique 3 of 18
Thermometer Bounds
Digits rise along a thermometer, starting at the bulb.
A Thermo sudoku technique.
How it works
A cell n steps from the bulb is at least n + 1, and a cell n steps from the tip is at most 9 − n.
A worked example
Thermometer: values must increase from the bulb, so the cell in row 9, column 9 (position 1 of 4) cannot be 5.
- The cells that make the pattern
- Candidates it rules out
A real position from a puzzle in the app. Small digits are the candidates the step looks at; coloured digits are already solved.
Practise it in Box Brain Sudoku
The app teaches Thermometer Bounds on this same board, then hands you puzzles that need it. When you are stuck mid-game, a hint first points you to the right area, then names the technique and shows the move.