Sparkfun Code Reference (automatically downloads code examples)
http://sparkfun.com/sikcode
Even if we don't end up using the SIK Code, its good practice to install the library. Open the readme.txt file to do it. After placing the SIK Guide Code in the folder specified in the readme.txt file, I had a problem with the spaces in the name of the file. I changed the name of the folder to SIK_Guide_Code and then it worked.
Graphical Resistance Calculator
http://www.dannyg.com/examples/res2/resistor.htm
Arduino Button 101 - Button circuit review
https://www.youtube.com/watch?v=XUuXq4J4u14
Mims Review - Electricity Basics
https://itp.nyu.edu/physcomp/lessons/electronics/electricity-the-basics/
Electrical Conductivity vs. Resistance
http://en.wikipedia.org/wiki/Electrical_resistivity_and_conductivity
