This in turn allows listeners to stay tuned to a network whilst travelling across the service area of multiple transmitters.
PI codes are not globally unique; ranges are assigned per-country, and are re-used in countries beyond FM radio range of each other.
For example, the first digit "C" as used in the BBC PI code example is used by the United Kingdom, Lithuania, Croatia, and Malta.
[1]: 69–72 They can be made globally unique by combining them with an ECC (extended country code).
PI codes are also used in Digital Audio Broadcasting as Station ID, and by the RadioDNS standard.