Changes

*[http://www.new.dli.ernet.in/rawdataupload/upload/insa/INSA_1/20005abc_47.pdf "Making Mountains out of Molehills? George Everest and Henry Barrow 1830-39"] by Jane Insley ''Indian Journal of History of Science'' 30 (1) 1995, pages 47-55. Henry Barrow was the first Mathematical Instrument Maker chosen by George Everest to set up and run a workshop for the repair of defective equipment for the Survey of India.

*[http://www.banglapedia.org/httpdocs/HT/L_0053.HTM Land Surveys] Banglapedia (National Encyclopaedia of Bangladesh). It is stated "The objectives of the revenue survey were to make accurate maps of the village boundaries and, sometimes, of the estate boundaries, showing topographical details, compiling certain statistical data for general administrative purposes, and making maps (usual scale: 4 inches = 1 mile and 1 inch = 1 mile) of each village and pargana"

===Historical books online===

*[http://books.google.com/books?id=tE41AAAAMAAJ&pg=PR1 ''A manual of surveying for India, detailing the mode of operations on the revenue surveys in Bengal and the North-western provinces''] by Ralph Smyth and Henry Edward Landor Thuillier 1851 Google Books