Normal sudoku rules apply. The grid starts mostly covered in fog. Placing some correct digits will cause the fog to be removed from some cells of the grid, revealing clues in those cells. Not all correct digits will reveal fog, and the fog may be anywhere in the grid. Digits on a line must be strictly between the digits placed in the circles at the ends of that line. Each line may only pass straight through a cell or have 90 degree turns. Lines may not cross or overlap, though may share circles at their ends. Each Between Line has a unique colour, though the circles are all the same colour as they may be shared. Digits separated by a black dot are in a 2:1 ratio.