The Franklin Institute
Frankin Institute Online: Group Graphing
This site from The Franklin Institute explores how to make a simple graph using a spreadsheet to portray survey data. It also gives a set of interesting sports-related web sites so that students can get statistical inforamtion.
Curated OER
Mathn stuff.com: Vertical Line Test
Defines the vertical line test and provides a diagram showing graphs which pass and fail the test. Also provides several links for further information.
Windstream
Ojk's Precalculus Study Page: Functions
An introduction to the basic terminology of functions, including how to use the vertical line test on the graph of a relation as a means of testing whether or not it is a function.