Can digits repeat on a thermometer?

No — values strictly increase, so each cell on a thermometer is larger than the previous one.

Where does a thermometer start?

At the bulb, the rounded end. Digits increase from the bulb toward the flat tip.

How long can a thermometer be?

Up to nine cells in a 9×9 grid (a 1-to-9 run), though most are shorter, which is what makes the range logic useful.

Thermometer Sudoku: Rules & How to Solve

Digits climb along each thermometer from bulb to tip. Learn how length alone pins down ranges of candidates.

The rule

Along each thermometer, digits must strictly increase starting from the rounded bulb and moving toward the flat tip. Standard sudoku rules apply everywhere else.

How to solve thermometer sudoku

Length sets the range

On a thermo with five cells, the bulb is at most 5 and the tip is at least 5 — every extra cell squeezes both ends inward.

The bulb is the floor

Because values only rise, the bulb holds the smallest digit on the thermometer. A long thermo forces a low bulb.

Chain across crossings

Where a thermo passes through a box you already know, propagate the increasing order to bound neighbours on both sides.

Frequently asked questions

Can digits repeat on a thermometer?: No — values strictly increase, so each cell on a thermometer is larger than the previous one.
Where does a thermometer start?: At the bulb, the rounded end. Digits increase from the bulb toward the flat tip.
How long can a thermometer be?: Up to nine cells in a 9×9 grid (a 1-to-9 run), though most are shorter, which is what makes the range logic useful.

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