Sudoku Variants Series (454) - Little Thermometers
(Published on 2. January 2026, 06:00 by Richard)
For this Sudoku Variants Project I have planned to publish a unique Sudoku variant every week.
Little Thermometers
Solve online in
I will see how long it takes before I am running out of ideas.
Apply classic sudoku rules.
Clues outside the grid indicate the presence of a thermometer that is fully placed in the direction of the arrow where all the digits on the thermometer add to the number of the clue and the bulb is always the closest to the clue. Digits on a thermometer are all different and strictly increasing from the bulb to the tip. Thermometers are mimimal three cells long and they include all possible digits. I.e.: the first digit behind the thermometer may not be larger than the last digit on the thermometer, and the last digit before a thermometer may not be smaller than the digit in the bulb.
Thermometers may overlap other thermometers.
Sudokupad (no answer check)
Sudokupad (with answer check)
or
Penpa+.
Solution code: Row 5
Comments
on 16. January 2026, 02:38 by QuiltyAsCharged
This is a great idea for a rule. I think it has more potential and it would be interesting to see a more challenging version, and/or to see how these thermos interact with other variants. Very nice puzzle!
on 5. January 2026, 15:35 by Ethos335
I've read through these rules so many times and I just dont get it
---
Reply: you have to place a thermometer in each of the diagonal directions indicated by the arrows. The bulb is closest to the arrow, so the digits increase from there. Each thermometer uses all possible digits in the indicated direction. I.e. After drawing the thermo's, there are no digits in front of it, of after it that could also be included in the thermo. (If 1-2-4-6-7 are placed in that order in the direction of an arrow, the given sum would be 20 and not 7, 12, 13, 17 or 19.)
All thermos have a minimum length of three cells.
Reply: For the 7 clue how do you make a 4 cell thermometer that sums to 7 that strictly increases, shouldnt the minimum sum be 10 (1-2-3-4)
---
Reply: It is clear that the thermo with a sum of 7 cannot be four cells long. So this one contains the digits 1-2-4 with the bulb in either R4C9 or R3C8.
on 3. January 2026, 12:14 by Franjo
Nice and tricky addition to the famous series. Thank you very much for creating and sharing this lovely puzzle.
on 3. January 2026, 06:01 by BorisTheSnake
Very nice logic, but despite the fast solve time, I'd say this is a 3*, probably the reason for the lower rating? The description of "behind the thermometer" is a little ambiguous as well. I'd write it as "first digit after a thermometer must be lower than the last digit on the themometer and the digit before a thermometer must be larger than the digit in the bulb."
---
Reply: Thx Boris.
About the disambiguation: I am open to other descriptions, but the first digit behind/after the thermo's may also be the same as the last digit on the thermo's. Hence: not larger.
About the rating: I have mixed emotions about the rating system here in the portal. A few of my thoughts / observations:
- There are a few notorious 'downgraders' active here in the portal. This puzzle has been solved by one of them.
- Some players hardly ever give a 'very nice' to my puzzles.
- I always hope that players don't look too much to the rating when chosing a puzzle to solve, but more to the puzzle itself and/or the author who has set it.
- Some players are more interested in my harder puzzles where discovering the intrinsic logic plays a bigger role, and may be disappointed by the 2-star ones. But the advent calendar has made me think of what I want with SVS. At the moment I try to keep the difficulty a bit lower, since it may attract more players, and one of my goals with SVS is making less known/obscure variants available for a larger group of players.
- Personally I think this is not the most brilliant puzzle I have created, so I can live with the current 91%. :)
on 3. January 2026, 01:44 by Chaossudokusplease
Great fun very approachable puzzle! I’ve gotten so used to your “easy versions” series recently that I’m actually a little bit disappointed there isn’t a harder second one for me to sink my teeth into after this!
---
Reply: Haha, thanks for this fun comment.
If you are in the mood for harder ones without an easier fellow puzzle there is plenty to discover if you sort the puzzles I have posted in descending difficulty rating. Otherwise you have to wait till the Advent period of 2026. I am seriously considering repeating such a calendar.
on 3. January 2026, 01:07 by dzamie
Wound up not really using the "all possible digits" rule, but I could see it getting used in a different puzzle with this rule.
---
Reply: Thanks. At least at one place this part of the ruleset is helpful, but I don't have tested it while ignoring it. Maybe the puzzle can be solved without it too.
on 2. January 2026, 09:06 by Piatato
Lovely! Became a lot smoother when I read the rules again and realized the minimum three cells requirement, haha!
