(3-1-3) UPC Modulo-10 Check Digit Algorithm

How do you calculate a MOD 10 check digit.

Step1:
Starting from position 1 of the number, add the values of the odd numbered position digits.

Step2:
Multiply by 3 the result of Step 1 above

Step3:
Starting from position 2 of the number, add the values of the even numbered position digits.

Step4:
Add up the results of Step 2 and Step 3

Step5:
The check digit corresponds to the smallest number which, when added to the results obtained through Step 4, gives a number which is a multiple of 10