Please go to the following site for revision

1. Construction of cross section
http://www3.moe.edu.sg/edsoftware/ir/files/geo-construction-of-cross-sections/index.htm

2.Contours and slope
http://www3.moe.edu.sg/edsoftware/ir/files/geo-contours-and-slopes/index.htm

3.Grid reference
http://www3.moe.edu.sg/edsoftware/ir/files/geo-grid-reference/index.html

4.Gradient
http://www3.moe.edu.sg/edsoftware/ir/files/geo-triathlon/index.html