The DRN - Decoder reference number, is a unique 11 or 13 digit number allocated by the manufacturer for each meter produced by the manufacturer. The DRN number starts with the manufacturer code (2 or 4 digits), and is followed by 8 unique digits and a single Luhn Check digit.

For 2 digit manufacturer codes: MMUUUUUUUUL

where: MM = manufacturer code, UUUUUUUU = serial number of the meter, and L = Luhn Check digit

For 4 digit manufacturer codes: MMMMUUUUUUUUL

where MMMM = manufacturer code, UUUUUUUU = serial number of the meter, and L = Luhn Check digit

Manufacturer codes are allocated by the STSA at the time of joining the STSA. Two digit manufacturer codes range from 01 to 99, whereas 4 digit manufacturer codes range form 0101 to 9999. Note that an allocated manufacturer code remains temporary (for a period of up to 2 years), or until such time as a product is certified by the STSA. Only then will the allocated manufacturer code become permanent. If a product is not certified within this 2 year period, the STSA reserves the right to reclaim the allocated manufacturer code and allocate that number to another member.

Since about 2015, only 4 digit manufacturer codes are allocated to members since all 2 digit numbers have been allocated.