Umbhalo Waphansi
a Elithi ISO liwukufushaniswa kweInternational Standards Organization; elithi ASA, limelela iAmerican Standards Association. Ezingxenyeni zeYurophu, kusetshenziswa nelithi DIN (Deutsche Industrie Norm). Ifilimu ehlelwe ngokuthi uISO 100/21 iwuASA 100, noma u-21 DIN.