Its learning by doing!!!
Get sample contour data [Shapefile format] from this link:
Open your arcmap, load this contour data in arcmap. Mine appear as:
Open the attribute table of contour layer. The elevation value of each contour is stored in field “contour” as below:
Now add field “index” in this table of type “short integer”. Just as shown below.
Right click on index column -> Field Calculatior -> choose python button -> double click on contour ->add % sign
I am gonna make video tutorial.
Here is the link for video. Its in swf format so you need swf player installed in your browser.
I ll be making youtube video later.