Subbranches have the same sorting code as the main bank office, but to uniquely identify them they have a two-digit suffix after the sorting code. Banks in Northern Ireland can be part of either the British or the Irish clearing system, depending on their country of registration. A sort code is the name given by both the British and Irish banking industry to the bank codes which are used to route money transfers between banks within their respective countries via their respective clearance organizations. Sortcodes are unique to the British and Irish banks for internal money transfers. The sort code, which is a six-digit number, is usually formatted as three pairs of numbers, for example 12-34-56. It consists of a four character header comprising an ISO 3166-1 alpha-2 country code, followed by two check digits that are calculated using a mod-97 technique and a country-specific Basic Bank Account Number (BBAN) of up to thirty alphanumeric characters.