Step 1: Divide the number into separate digits:
0899 => 0 8 9 9
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
0 to 8 = 8
8 to 9 = 1
9 to 9 = 0
9 to 0 = 9
Step 3: Combine the filters to a string:
8 1 0 9 = 8109