Thermo Sudoku

Digits increase as you move away from each bulb.

Rules

Follow standard row, column and box rules. Along each thermometer, digits strictly increase from the round bulb toward the tip. They need not be consecutive. Read any extra instructions for branching thermometers or other added constraints.

A visual example

Thermo Sudoku example diagram — The illustrated four-cell thermometer contains 1, 2, 3 and 4 from bulb to tip. It could also contain 1, 3, 6 and 8. On any four-cell thermometer, the bulb is at most 6 and the tip is at least 4, because three distinct larger or smaller digits must fit.

How to start

Use thermometer length to bound candidates before placing digits. If the second cell of a four-cell thermometer is 6, the two cells after it must form an increasing pair from 7, 8 and 9. Check those possibilities against their rows, columns and boxes, then revisit the earlier cells.

A mistake to avoid

Increasing does not mean increasing by one. Do not fill a thermometer as a consecutive run unless the other constraints prove it.

Keep learning

Review the standard rules and worked solving techniques. Our daily game and printable packs use standard Sudoku rules; they do not play this variant.