First of all I am not sure if I am in the right place to post a comment on the ebook of Lessons In Electric Circuits. If I am not I would appreciate very much if I could be guided to place this comment. If I am, here is my comment. It is about Volume II Chapter 6 "Resonance" Section 1" An Electric Pendulum". Almost at the end of the section, the author displays a graph of the KE and PE of a mechanical pendulum. The graph tries to show that as PE increases KE decreases and vice versa. So far so good. My comment is that the graph show a dotted line in the middle of the y-axis which gives the impression that energy can be negative. Further the 2 curves appear to be of two sinusoidal separated by 90 degrees which is not the case. One of them is the square of cosine function and the other is the square of a sine function. Thanks