Click a number to remove it. Tap it again to return a deleted number to the field. Click and hold the number or double-click to lock it. If you know that a particular number needs to be used, you can lock it on to make solving the rest of the puzzle easier. "Solution" button is available without restriction. All the tasks are divided into 5 categories of dimension (5x5, 6x6, 7x7, 8x8, 9x9). Each group has 1000 levels. There are total (5x1000) = 5000 tasks.