individual serial number C → control digit Found on: Bulgarian ID card or passport Birth certificate Tax documents Social security and healthcare records • https://www.oecd.org/content/dam/oecd/en/topics/policy-issue-focus/aeoi/bulgaria - tin.pdf • http://www.nra.bg/ Croatia Personal Identification Number (PIN); Croatian: Osobni identifikacijski broj (OIB) Digits: 11-digit Format: 99999999999 (10 digits are randomly chosen, while the 11th digit represents the control number calculated by "Modul 11.10", ISO