illustrate the three methods of showing scale
Since this is not my area of expertise, I searched Google under the key words "methods of showing scale" to get these possible sources:
https://www.google.com/search?client=safari&rls=en&q=methods+of+showing+scale&ie=UTF-8&oe=UTF-8
In the future, you can find the information you desire more quickly, if you use appropriate key words to do your own search. Also see http://hanlib.sou.edu/searchtools/.
http://www.hackcollege.com/blog/2011/11/23/infographic-get-more-out-of-google.html