I got a question regarding ground in terms of a power supply and another one with regards to PCBs. Usually you see people put a jumper cable between the negative terminal of a power supply to common ground. Why do people do this? Is it for the user to reference the power supply to actual earth ground? Isn't the chassis tied to earth ground using the third prong? Whats the difference between digital ground and analog ground in terms of a PCB? How are things actually wired in terms of a layout file?