General maintenance principles : maintenance of international transmission systems and telephone circuits: recommendations M.10 - M.782 / International Telecommunication Union
Maintenance of international telegraph, phototelegraph and leased circuits : maintenance of the international public telephone network: maintenance of maritime satellite and data transmission systems: recommendations M.800 - M.1375 / International Telecommunication Union
NP EN 29001 : sistemas de qualidade: modelo de garantia da qualidade no projecto/desenvolvimento, produção, instalação e após venda: 1988 / Instituto Português da Qualidade