Step 1: Divide the number into separate digits:
6702 => 6 7 0 2
Step 2: Calculate the distance between each digit and the next (the last digit with the first):
6 to 7 = 1
7 to 0 = 7
0 to 2 = 2
2 to 6 = 4
Step 3: Combine the filters to a string:
1 7 2 4 = 1724