Step 1: Divide the number into separate digits:
0677 => 0 6 7 7
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 7 = 0
7 to 0 = 7
Step 3: Combine the filters to a string:
6 1 0 7 = 6107