Porter, Lindsay
Haynes Publishing, 1991
Buku Referensi
Michael G. Grantham, editor
Routledge, 2011
Buku Teks
White, Charles
Haynes Publishing, 1992
Buku Referensi
Porter, Lindsay
Porter Publishing, 1995
Buku Referensi
Farnell, Warren M.
Pearson-Prentice Hall, 2006
Buku Teks