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B [N] IMEI Check Digit computation
B.1 Representation of IMEI
B.2 Computation of CD for an IMEI
B.3 Example of computation

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The International Mobile station Equipment Identity and Software Version number (IMEISV), as defined in clause 6, is a 16 digit decimal number composed of three distinct elements:

- an 8 digit Type Allocation Code (TAC);
- a 6 digit Serial Number (SNR); and
- a 2 digit Software Version Number (SVN).

The IMEI is complemented by a check digit as defined in clause 3. The Luhn Check Digit (CD) is computed on the 14 most significant digits of the IMEISV, that is on the value obtained by ignoring the SVN digits.
The method for computing the Luhn check is defined in Annex B of the International Standard "Identification cards - Numbering system and registration procedure for issuer identifiers" (ISO/IEC 7812 [3]).
In order to specify precisely how the CD is computed for the IMEI, it is necessary to label the individual digits of the IMEISV, excluding the SVN. This is done as follows:
The (14 most significant) digits of the IMEISV are labelled D14, D13 ... D1, where:

- TAC = D14, D13 ... D7 (with D7 the least significant digit of TAC);
- SNR = D6, D5 ... D1 (with D1 the least significant digit of SNR).

Computation of CD from the IMEI proceeds as follows:
Step 1:

Double the values of the odd labelled digits D1, D3, D5 ... D13 of the IMEI.

Step 2:
Add together the individual digits of all the seven numbers obtained in Step 1, and then add this sum to the sum of all the even labelled digits D2, D4, D6 ... D14 of the IMEI.

Step 3:
If the number obtained in Step 2 ends in 0, then set CD to be 0. If the number obtained in Step 2 does not end in 0, then set CD to be that number subtracted from the next higher number which does end in 0.

IMEI (14 most significant digits):

TAC SNR D14 D13 D12 D11 D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 2 6 0 5 3 1 7 9 3 1 1 3 8 3Step 1:

2 6 0 5 3 1 7 9 3 1 1 3 8 3 x2 x2 x2 x2 x2 x2 x2 12 10 2 18 2 6 6Step 2:

2 + 1 + 2 + 0 + 1 + 0 + 3 + 2 + 7 + 1 + 8 + 3 + 2 + 1 + 6 + 8 + 6 = 53Step 3:

CD = 60 - 53 = 7