Silas - 2005.08.18
Suppose you have first 12 digits of EAN-13 barcode. You'll have to calcule the 13th digits, which is the checksum digit. I did a little proc that makes it for you:
proc checksum {first12digits} {
set total 0
for {set i 0} {$i < 12} {incr i} {
set multiplicator [expr ($i % 2 == 0) ? 1 : 3]
incr total [expr [string index $first12digits $i] * $multiplicator]
}
set checksum [expr 10 - ($total % 10)]
return $checksum
}