Thermo Sudoku (PuzzleMadness)

About Thermo Sudoku (PuzzleMadness)

Thermo Sudoku follows the normal sudoku rules, so each row, column and 3x3 box holds 1 to 9 once each. The extra clues are thermometers: shaded paths with a round bulb at one end that wind through neighbouring cells. Reading from the bulb towards the far end, every digit has to be larger than the one before it. The digits do not have to be consecutive, only strictly increasing.

Long thermometers are the strongest clues, since a path of six cells leaves little room: its bulb can be at most 4 and its tip at least 6. Today's Medium grid, for example, has more than a dozen thermometers of different lengths alongside its given digits.

The grid works like every sudoku on PuzzleMadness: number buttons above and below it, an eraser, and a pencil mode for candidate digits. On a keyboard, the number keys enter digits, the arrow keys move between cells, Ctrl, Shift or Alt with a number adds a pencil mark, and Delete or Backspace clears a cell.

PuzzleMadness is a free puzzle website run by Dewi, a software developer who started out making games for the PlayStation 2, Nintendo Wii and DS and now builds the site as a hobby. It carries dozens of puzzle types, from classic sudoku to newer logic grids, and each one gets its own dated puzzle every day at each difficulty. Thermo Sudoku comes in Easy, Medium, Hard and Tough versions plus a Mixed page, and the same day's Thermo Sudoku puzzle is shared by everyone who opens it.

The site checks your grid as you go and tells you when it is finished; it does not publish solutions. Each completed puzzle earns a score, and scores feed a monthly and an all-time Thermo Sudoku leaderboard, where only your best attempt at a puzzle counts. Older days stay in the archive, so a missed puzzle can still be played later and still counts toward the current month. Playing needs no account; a free registration gives you a username on the leaderboards and a cloud save. The pages carry adverts.

How to play Thermo Sudoku (PuzzleMadness)

1. Open today's Thermo Sudoku page on PuzzleMadness and choose a difficulty from the menu above the grid.
2. Click a cell and enter a digit with the number buttons above and below the grid or with the keyboard; the eraser button clears a cell.
3. Fill every row, column and 3x3 box with the digits 1 to 9, each once.
4. Along each thermometer, make the digits strictly increase from the round bulb to the other end.
5. Turn on pencil mode (the pencil button, or Ctrl, Shift or Alt with a number key) to jot candidate digits in a cell.
6. The site tells you when the grid is complete and adds your score; registered players appear on the leaderboards.

Screenshots

Tips

• On a thermometer of length n, the bulb can be no higher than 10 minus n and the tip no lower than n.
• A given digit in the middle of a thermometer caps every cell before it and sets a floor for every cell after it.
• Where two thermometers share a bulb or cross a box, compare their limits to narrow the candidates.
• Missed a day? Earlier puzzles are in the archive, and finishing one still counts toward this month's leaderboard.

Questions