Step 1: Divide the number into separate digits:
0678 => 0 6 7 8
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
0 to 6 = 6
6 to 7 = 1
7 to 8 = 1
8 to 0 = 8
Step 3: Combine the filters to a string:
6 1 1 8 = 6118