Step 1: Divide the number into separate digits:
7903 => 7 9 0 3
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
7 to 9 = 2
9 to 0 = 9
0 to 3 = 3
3 to 7 = 4
Step 3: Combine the filters to a string:
2 9 3 4 = 2934