I'm curious to learn more about the Image Transmission Settings screen for my P3A. There is an "Auto" and "Custom" toggle on the screen along with a graph: the vertical column are numbers -100 to -60 under the heading RSSI(d). What is that? The horizontal column are the channel number 13 through 20. I suppose the Auto setting is testing the channels and choosing the ones with the best signal? What are the pro and cons of the Auto setting and the Custom setting? There are the green, red and blue indicators of signal stability...they seem to change...why is that?