Robot Arms and 2D Coordinate Frames

I have mentioned here that I want an applied robotics book. One of the many excellent suggestions I received was for Peter Corke's Robot Academy. Given a little bit of free time, I started watching the videos and got hooked. It was just the right combination of math and theory with practical implementation. However, it moves fast enough that I need to take notes so I can come back to it after taking a break (to do work). 

Here are some of my notes about 2D coordinate frames for robot arms.