Sources Used:

                                   http://www.spc.noaa.gov/faq/tornado/

                                   http://www.therichest.com/expensive-lifestyle/location/top-10-deadliest-tornadoes-in-world-history/

                                   http://worldnews.about.com/od/disasters/tp/Worlds-Worst-Tornadoes.htm

                                   http://www.ehow.com/info_8297640_tools-used-measure-tornadoes.html

                                   "Tornadoes" (Kids Discover Magazine)

                                     Hurricanes and Tornadoes By: Neil Morris (1998)

                                     Library of Natural Disasters Tornadoes By: World Book (2009)

                                     World Book By: World Book (1999) (T)