How to Calculate a Modulo 10 Check Character.
Modulo 10 check characters are used with various barcode symbologies. They are always used with UPCA and EAN13 barcodes. We get quite a number of inquiries as to how to calculate this digit. So here is the procedure.
Try this on a few UPC or EAN symbols that have the check digit already printed with the symbol, just to make sure you've got the process correct. If you've got a code with the digit already printed, make sure not to include it in your calculations. Remember, with UPC there should be eleven digits involved in the calculation. Twelve with EAN. 
