Grid Gravity

How to play Grid Gravity

Touch controls: Tap any square to raise its tower; each square is at least 44 pixels across and 46 pixels high even on a 320 pixel wide screen, the grid is one object with no controls to aim at precisely, and nothing scrolls sideways on any phone size.

Keyboard controls: Arrow keys and W A S D move the cursor between squares, keys 1 to 4 set the height of the square under the cursor, 0 or Backspace clears it, N clears the whole grid, Enter or Space starts a run from the title or the end screen, P or Escape pauses and resumes, R restarts, M toggles sound.

Screen: This game works best in any orientation.

About Grid Gravity

Grid Gravity is a sightline puzzle, sometimes called a skyscraper grid. A four by four plot has to be filled with towers one, two, three and four storeys tall so that no height repeats in any row or column, and the numbers around the edge say how many towers can be seen from that direction. A tall tower hides every shorter tower behind it, so a clue of 1 means the nearest tower is the four storey one, and a clue of 4 means the heights march upwards in order.

Each grid in the run was checked by searching every four by four arrangement that fits the clues, and only grids with exactly one answer were kept. The first two grids show all sixteen clues and teach the rule; the last two hide six of them, which turns the puzzle from reading into genuine deduction.