1) Initialize a sum variable to the value of your Start code (Start A = 103, Start B = 104, and Start C = 105).
2) Initialize the Weighting value to 1.
3) Starting with the first character in your bar code after the Start code (working from left to right), look up the Value associated with that character and multiply that value by the Weighting value.
4) Increment the Weighting value by 1, and add the result of the calculation above to your sum variable.
5) Repeat this until there is no more data, then divide the sum variable by 103. The remainder from this calculation is the checksum. Convert the Value to a character via Tables 2 - 4.
6) Put the checksum character after your data and end the bar code with the Stop code character (~).
7) Note that both the sum and the checksum variables for any bar code can be displayed by our Bar128 utility program.