› Useful tips » To view the statistics about the current puzzle, click Game ▸ Puzzle Statistics.
GNOME Sudoku ranks puzzles based on the number of cells that can be rapidly filled.
The puzzle statistics box shows:
the overall difficulty
the number of cells which can be filled by elimination, starting from the blank grid (i.e. only a 2 can go in this box, so it must be a 2)
the number of cells that can be filled by the process of filling, starting from the blank grid (i.e. only one cell in this row can be a 2, so it must be a 2)
the number of times in solving the puzzle that the program used the trial-and-error algorithm to solve the puzzle
All sudoku puzzles can be solved without ever having to guess. When the statistics box says that Sudoku used trial-and-error X number of times, it does not mean that a human would have to use trial-and-error to solve the puzzle.