How Many Different Differences?
The brief
Normal 6x6 sudoku rules apply.
The circled digit on a line indicates how many DISTINCT differences exist between pairs of adjacent digits along that line. Eg: A line that reads 6425136 has adjacent pairs whose differences are 2,2,3,4,2,3 respectively. Therefore, the digit 3 on the line would be circled, because there are 3 distinct differences (2, 3 and 4).
No two circles contain the same digit.