Harvard Business School, 1997
Buku Teks
Friedl, Alfred E, author
McGraw-Hill, 2001
Buku Teks
Kelly, Francis J.
Warner Book, 1986.
Buku Teks
McGraw-Hill Book Company, Inc., 1954
Buku Teks
Erlinda Muslim, author
Fakultas Teknik Universitas Indonesia, 2014
UI - Laporan Penelitian