I have a €20 note with serial number U02401890701. When I add up the digits I get a sum of 32 which is 3+2 = checksum for France. OK. The national code is "U" for France and it has a printing code of 'E" which is also France.

I have a €5 note with serial number X00025041809. When I add up the digits I get 29 which gives 2 + 9 = 11. With double digits supposed to use only first digit but that is 1 which is a "2". ???? The "X" is the national code for germany and the printing code is "P" which is also Germany. My question is why didn't I come up with a checksum of 2?