Step 1: Divide the number into separate digits:
6944 => 6 9 4 4
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
6 to 9 = 3
9 to 4 = 5
4 to 4 = 0
4 to 6 = 2
Step 3: Combine the filters to a string:
3 5 0 2 = 3502