The Decoder Reference Number, also known as a the meter number, or the IndividualAccountIdentificationNumber (IAIN), is a number that uniquely identifies a payment meter globally, and is made up as follows:

DRN = [manufacturer code] [serial number] [check digit]

The DRN may be 11 digits (for 2-digit manufacturer codes), or 13 digits (for 4-digit manufacturer codes). [IEC62055-41]

The serial number, also known as the Decoder Serial Number (DSN), is an 8-digit sequential number generated by the manufacturer of the payment meter.

The check digit is calculated, using the Luhn formula, from the previous digits of the DRN and appended as the final digit of the DRN. [Wikipedia].