Step 1: Divide the number into separate digits:
7994 => 7 9 9 4
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 4 = 5
4 to 7 = 3
Step 3: Combine the filters to a string:
2 0 5 3 = 2053