Step 1: Divide the number into separate digits:
06908 => 0 6 9 0 8
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
0 to 6 = 6
6 to 9 = 3
9 to 0 = 9
0 to 8 = 8
8 to 0 = 8
Step 3: Combine the filters to a string:
6 3 9 8 8 = 63988