Thermometers Puzzle Online
Thermometers is a row-and-column logic puzzle built around one simple physical rule: Mercury always fills continuously from the bulb toward the tip. The challenge comes from combining that one-way fill rule with exact row and column totals across a board containing many separate straight and curved thermometers.
How Thermometers works
Every cell belongs to exactly one thermometer. A thermometer has a bulb, a path, and a tip. Its Mercury level can be zero, completely full, or anywhere in between. What it cannot do is leave a gap. If a cell is filled, every earlier cell on that same thermometer toward the bulb must also be filled. If a cell is known to be empty, every later cell toward the tip must also be empty.
Numbers beside the rows and above the columns tell you the exact number of Mercury cells that must appear there when the puzzle is finished. You are not trying to guess a hidden picture. You are finding one consistent fill level for every thermometer so that all row counts, all column counts, and every bulb-to-tip continuity rule hold simultaneously.
The playable specialist uses three sizes: Easy 6×6, Standard 8×8 and Challenge 10×10. The frozen source bank contains 20 independently unique boards at each size. Paths are generated inside the project and include curved thermometers rather than relying on a board pack or remote puzzle API.
The first deductions to look for
Rows or columns with zero
If a clue is zero, every cell in that line is empty. Because Empty marks propagate toward thermometer tips, one zero clue can eliminate several later cells on a curved thermometer and immediately tighten another row or column.
Rows or columns already at their target
Suppose a row needs three filled cells and you have already proved three Mercury cells there. Every remaining unknown cell in that row must be empty. This is one of the most reliable deductions in the puzzle because it depends only on the exact row total.
Rows or columns where all remaining unknown cells are needed
If a row needs five Mercury cells, currently has three, and has exactly two undecided cells left, both unknown cells must be Mercury. The same logic works in columns. Filling one of those cells may also fill earlier cells toward a bulb, so always re-check the crossing counts after a forced placement.
Thermometer range deductions
A Mercury mark at position four means the fill level cannot be lower than four. An Empty mark at position six means the level cannot reach six. Combining these facts gives each thermometer a remaining local range. If the minimum and maximum meet, the entire thermometer has one locally possible fill level and its undecided cells can be resolved without revealing the answer.
Why curved thermometers matter
An all-horizontal Thermometers board can become too close to solving independent row segments. Curved paths create stronger interactions because one thermometer level can add Mercury to several different rows and columns. A single turn can make the same thermometer responsible for satisfying part of one row, then part of one column, then another row.
The V0.125 generator starts from complete orthogonal path covers and cuts them into separate thermometers of controlled lengths. Easy boards use shorter paths. Standard boards use longer paths with more turns. Challenge boards allow substantially longer curved paths so the 10×10 solver does not explode into dozens of tiny independent variables. This design choice improves both puzzle character and the cost of proving uniqueness.
Every source stores the solved fill level for each thermometer only as frozen verification data. The public game starts with an undecided board. A separate exact solver counts legal assignments under the row, column and monotonic fill rules and rejects a candidate source unless the legal solution count is exactly one.
Use the live deduction monitor
The game does more than show a static grid. Row and column counters report your current Mercury count against each target. Impossible lines are highlighted when they are overfilled or can no longer reach the clue with the remaining unknown cells.
Each thermometer also receives a fill-level chip. A chip such as 2–5/7 means that, from your current Mercury and Empty marks, the thermometer can locally contain between two and five filled cells out of seven total. A chip such as 4/7 is forced: only fill level four remains locally consistent with your current marks.
This monitor is deliberately described as local. It does not pretend that every remaining level shown can necessarily extend to a complete global solution. That distinction matters for trust. The independent solver proves the frozen source has one complete solution; the live monitor explains immediate deductions from the state you have actually entered.
Technique-aware Verified Hint
Verified Hint is designed to teach before it reveals. It first checks whether one of your existing decided cells conflicts with the unique verified reference and repairs that conflict. If the current marks are consistent, it searches for a saturated row or column, a row or column that needs every remaining unknown cell, or a thermometer whose local fill-level range has collapsed to one value.
Only when those immediate techniques do not produce a step does the helper reveal one cell from the unique verified solution. Using Check or Verified Hint marks the run Assisted, so a clean solve remains meaningfully different from a solve completed with answer support.
Undo and Redo are available throughout an active run. The browser also autosaves the board, move history and elapsed time locally. No account, cloud database or paid puzzle service is required.
Input designed for desktop and mobile
Cycle mode lets you move through Unknown, Mercury and Empty with a tap or keyboard action. Mercury paint is faster when you already know a group of cells must fill; dragging over a cell fills that thermometer continuously back toward the bulb. Empty paint works in the opposite direction, marking the chosen cell and every later position toward the tip empty.
Desktop right-click provides a quick Empty mark. Keyboard players can use arrow keys to move, M for Mercury, X or E for Empty, Space to cycle and Ctrl/Command Z for Undo. The grid is sized to stay within narrow mobile viewports and the clue counters remain adjacent to the puzzle instead of disappearing into a desktop-only sidebar.
Practice, replay and Daily Thermometers
Practice URLs stabilize with a seed, so refreshing the same URL reproduces the same source and symmetry transform instead of silently changing the puzzle. The 60 frozen sources support eight square symmetries, creating 480 verified source-transform starts without claiming that every possible Daily date must be globally unique.
Daily Thermometers uses a separate date-stable selection. It maintains its own local history and specialist streak and stays outside Today’s 6. This means you can make Thermometers a daily habit without changing the platform’s frozen six-game rotation contract.
For a full puzzle now, open the Thermometers game. For the date-stable mode, open Daily Thermometers. You can also return to My Mix or browse the broader logic game collection.