List of sources:
Google scholar. http://scholar.google.co.za Publications by H.W. Gordon.
Liebenberg, E.C. Die topografiese kartering van Suid-Afrika, 1879-1972: 'n Histories-geografiese ontleding (pp. 85-86). MA-verhandeling in geografie, Universiteit van Suid-Afrika, 1973.
National Automated Archival Information Retrieval System (NAAIRS). http://www.national.archives.gov.za/naairs.htm Documents relating to Captain (HW) Gordon.
Robinson, W.B. Discussion of the geodetic position of Mr Melvill's astronomical station at Johannesburg, and the connection between the Rand system of surveys and the geodetic system. Journal of the Institute of Land Surveyors of the Transvaal, 1907, Vol. 1(5), pp. 175-183.
Rousseau, D.P.M. South African control surveys from Maclear to the present. Transactions of the Royal Society of South Africa, 1995, Vol. 50(1), pp. 79-88.
Zakiewicz, T. The African Arc of the 30th Meridian. South African Journal of Surveying and Mapping, 1997, Vol. 24(2), pp. 65-82.