The lightning bolt has always been a symbol of the Boy Who Lived and the magical world he lives in. As such an icon, it just had to be part of the CAL! (Personally, I think it would look equally good in red!)
The PDF contains graphs (with arrows!) and written instructions for the square. The square is designed to be worked from the lower right-hand corner up to the upper left-hand corner.
I will be posting the graphs for our other alternate squares later this week. (There are some great things to come, so stay tuned for more updates!