Step 1: Divide the number into separate digits:
6373 => 6 3 7 3
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
6 to 3 = 3
3 to 7 = 4
7 to 3 = 4
3 to 6 = 3
Step 3: Combine the filters to a string:
3 4 4 3 = 3443