Normal sudoku rules apply. Blue dots join cells with a difference equal to the grey central digit of their box. (For example, if r2c5=4 then r2c4 - r3c4 = ± 4)
Normal sudoku rules apply. Blue dots join cells with a difference equal to the grey central digit of their box. (For example, if r2c5=4 then r2c4 - r3c4 = ± 4)