Bulb to tip
Let the thermometer narrow your next move
Thermo Sudoku follows the usual row, column and box rules, with one extra condition: digits strictly increase along each thermometer from bulb to tip. They may skip numbers. The path’s length limits which digits can fit at each position.
01
Count cells along the path
Include the bulb when counting. A five-cell thermometer starts no higher than 5 and ends no lower than 5, before other Sudoku restrictions apply.
02
Use a known middle digit
If the third cell of a five-cell thermometer is 7, the final two cells must be 8 and 9. Smaller digits belong before it.
03
Read the path in both directions
After any placement, check earlier cells for smaller possibilities and later cells for larger ones. Then revisit the affected rows, columns and boxes for singles.