# S10 (UPU standard)

The UPU S10 standard defines a system for assigning 13-character identifiers to items for the purpose of tracking and tracing them during shipping.

The identifiers consist of a two letter service indicator code, an eight digit number, a check-digit, and a two-letter ISO country code, the latter identifying the issuing postal administration.[1]

With increased liberalization and the possibility of multiple postal services operating in the same country, the use of country codes to designate the postal service is a problem. To solve this, each country has a designated postal service that controls all S10 identifiers from that country; any competing postal services will have to cooperate with the designated owner.

Code Interpretation[2]
AA-AZ Letter post: recorded delivery, but neither registered nor insured
BA-BZ for domestic, bilateral, multilateral use only
CA-CZ Parcel post
DA-DZ for domestic, bilateral, multilateral use only
EA-EZ EMS
GA for domestic, bilateral, multilateral use only
GD for domestic, bilateral, multilateral use only
LA-LZ Letter post: express / Exprès delivery
NA-NZ for domestic, bilateral, multilateral use only
PA-PZ for domestic, bilateral, multilateral use only
RA-RZ Letter post: registered, but not insured delivery
UA-UZ Letter post: items other than AA-AZ, EA-EZ, LA-LZ, RA-RZ, VA-VZ, subject to customs control, i.e. bearing a CN 22 or CN 23
VA-VZ Letter post: insured delivery
ZA-ZZ for domestic, bilateral, multilateral use only

The check-digit is calculated as follows :

```Ignore the Service Indicator Code and Country Code
Assign the weights 3,4,5...10 to the 8 digits, from left to right
Calculate S, the sum of each digit multiplied by its weight.
For example, for the number 11112222, S = 1*3 + 1*4 + 1*5 + 1*6 + 2*7 + 2*8 + 2*9 + 2*10
Calculate the check digit, C, from C = 11 - (S mod 11)
If C = 10, change to C = 0
If C = 11, change to C = 5
```