Step 1: Divide the number into separate digits:
7995 => 7 9 9 5
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
7 to 9 = 2
9 to 9 = 0
9 to 5 = 4
5 to 7 = 2
Step 3: Combine the filters to a string:
2 0 4 2 = 2042