Signal Grid: count useful presses, not just lit lamps
Compare three, five and six illuminated squares to see why a darker board need not be closer to completion, and what the starting minimum actually measures.
Worked examples use the Standard board unless a different size is stated. Hard and Expert may change the board dimensions or amount of information to track.
Brightness and distance answer different questions
A tempting progress measure in Signal Grid is simply the number of illuminated squares. It is visible and easy to count, but it ignores how the switches overlap. The game instead displays the minimum number of presses needed by the starting board. That minimum stays attached to the starting position; the live move counter records the route you have chosen.
One press does not always change the same number of lamps. A corner affects three, a non-corner edge affects four and an interior square affects five. Consequently, two equally short puzzles can begin with different amounts of light. Turning off more lamps with a move is useful only if the remaining pattern can also be explained.
Compare two one-press teaching positions
Imagine a separate unlit five-by-five teaching board after its top-left corner has been pressed once. Three lamps light up: row 1 column 1, row 1 column 2 and row 2 column 1. Pressing that corner again clears them, so the minimum is one. It cannot be zero because the board is not already clear.
Imagine the same calculation from an unlit board, this time after pressing the centre at row 3 column 3. Five lamps light up, yet the same centre press clears them in one move. Five lit lamps are therefore not necessarily farther from the goal than three. These small examples explain the metric; Hard’s generated starting boards have a higher minimum than either example.
Prove a two-press case without guessing
From an unlit five-by-five board, press row 3 column 3 and row 3 column 4. Their neighbourhoods overlap at those two centre squares, which change twice and finish unlit. Six lamps remain: row 2 columns 3 and 4, row 3 columns 2 and 5, and row 4 columns 3 and 4.
Repeating the two stated presses clears this position. No single press could have created its six lit squares, because a press affects at most five. Since the position is neither clear nor one press from clear, and a two-press route exists, its exact minimum is two. This argument combines a lower bound with a concrete route rather than relying on how bright the board looks.
Use the budget to review a route
If the starting minimum is ten and your route has already used twelve presses, the puzzle is still playable. You have only learned that this route cannot finish at the original minimum. There is no countdown or automatic failure. Undo reverses the last press and its move count; Restart restores the initial lamps so a different route can be compared on the same problem.
Repeated presses at one square cancel in pairs, but both accepted presses add to the counter unless you undo them. Before chasing a lower count, explain which lamps each planned press changes and which overlaps cancel. The starting minimum is a useful reference, while a complete solution still requires every lamp to finish off.
An original guide for this site's implementation. Found an unclear step? Let us know.