Arntz, Helmut
The Press and Information Office of the federal Germa Govermant, [1967]
Buku Teks
Kohnke, Helmut
Tata McGraw-Hill, 1980
Buku Teks
Fellen
Fakultas Teknik Universitas Indonesia, 2004
UI - Skripsi (Membership)
Callis, Helmut G.
Henry Holt and Company, 1959
Buku Teks
Munchen Deutscher Taschenbuch 2002
Buku Referensi