mechanism for GTIN-13 is the same for Global Location Number/GLN.

For instance, the UPC-A barcode for a box of tissues is "036000241457". The last digit is the check digit "7", and if the other numbers are correct then the check digit calculation must produce 7.
# Add the odd number digits: 0+6+0+2+1+5 = 14.
# Multiply the result by 3: 14 × 3 = 42.
# Add the even number digits: 3+0+0+4+4 = 11.
# Add the two results together: 42 + 11 = 53.
# To calculate the check