Step 1: Divide the number into separate digits:
9330 => 9 3 3 0
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
9 to 3 = 6
3 to 3 = 0
3 to 0 = 3
0 to 9 = 9
Step 3: Combine the filters to a string:
6 0 3 9 = 6039