1. A return always means a straight face
This is the key to the game. A straight face sends the wave straight back, and the wave then retraces its whole path to the entry port. A slanted face, by contrast, only turns the wave through a right angle.
That gives two rules, which we checked with the game's engine on thousands of random fields:
- a wave that comes back hit at least one straight face;
- a wave that comes out elsewhere only touched slanted faces.
Direct consequences: a wave that comes out elsewhere never touched the bar, which has only straight faces. And the diamond, whose faces are all slanted, can never cause a return on its own.
2. A white wave straight across means a clear line
A wave that comes out directly opposite its entry, in white, has most likely crossed an empty row or column. That is valuable early in the game: it rules out eight cells at once.
If a white wave comes out anywhere other than opposite, a white module deflected it. Since white does not tint the wave, this is often the only way to locate it.
3. Decode the colour as a mix
Each coloured module adds its colour once, even if it is hit several times. Purple means red and blue, orange red and yellow, green blue and yellow, black all three primaries.
Since you know each module's colour, the wave's colour tells you which of the coloured modules it touched. A green wave must have met the blue module and the yellow one, whatever its route. With two modules of the same colour, the reasoning gets subtler: the wave touched at least one of them.
4. Probe to test an idea, not to sweep
Firing waves at random all round the edge is expensive. It is better to form a hypothesis, then choose the probe that confirms or rules it out.
Neighbouring probes are a powerful way to measure a module. In the commented game of our beginner's guide, two red returns on columns 2 and 4 are enough to prove the bar is horizontal: a vertical bar is only one cell wide.
5. Count blocked ports as information
A wave follows the same path in both directions. That is why both ends of a known signal are blocked: a deflected wave tells you about two ports at once, whereas a return only covers one.
Before probing, ask yourself what the chosen port can still teach you. If your hypothesis already predicts the exit with certainty, the probe only confirms it: save it for when you are genuinely unsure.
6. Place your hypotheses as you go
Modules placed on the field are free and stay on your device, even if you reload the page. Place them as soon as an idea takes shape, then check every signal in the history against your layout.
Tap a line in the history to highlight it and trace the wave's path over your hypothesis in your head. If a single exit or colour does not match, your layout is wrong.
7. Only submit once everything adds up
A wrong submission costs 2, as much as two probes, and tells you nothing about what is wrong. Submit only when every signal in the history is explained by your layout.
Good news: the game accepts any solution that gives exactly the same exits and colours as the real field on all 32 ports. If two layouts remain possible, guessing or probing comes out the same on average. With more than two, a probe that separates them costs less than a series of submissions.
How does the score reward precision?
The score shown during play is your cost: a probe is worth 1, a wrong submission 2. Up to a cost of 4, performance is at its maximum; each point beyond that takes off 5%, with a floor of 30%.
Time does not count at all: take your time to reason before each probe. There is no joker either, so no shortcut pays off.
Going further
If you know Black Box, Eric Solomon's deduction game where you hunt for atoms hidden on an 8×8 grid, Ondulo is in the same spirit, with shapes and colours. For more puzzles of this kind, see our pick of daily logic games, or try Mindo, where you also deduce a hidden code from clues.