Standard DIN 1304-1, Publication date: 1989-03 Letter symbols for physical quantities; symbols for general use

Standard DIN 1304-6, Publication date: 1992-05 Letter symbols for physical quantities; symbols to be used in electrical communication technology

Standard IEC 60027-1, Publication date: 1992-12 Letter symbols to be used in electrical technology; part 1: general

IEC 60027-2A, Publication date: 1975 Letter symbols to be used in electrical technology; part 1: general