Here's a puzzle worthy of Sudoku where you have to find the location of rounds on the corners of a grid boxes encrypted. The principle is simple, but the resolution of the grid is a little less, especially 5 × 5 squares.
Fill or empty the rounds with the mouse. Once you think you have solved the grid, click the Check button.
A context menu should be shown when right-clicking or, on touch devices, long-pressing in the game. This menu especially allows to play in full screen and control the volume.