There is one thing I wanna confirm here. As we know, Pico have four coloured BNC test leads, blue,red,green &yellow. I suppose blue used for CHA, red for CHB, green for CHC, yellow for CHD. While we are connecting blue lead to CHA and the fixed ground cable of blue connecting to battery negative, then CHB&CHC&CHD don't need to ground again with their removable ground cables. Am I right?
Should you be testing multiple, what are perceived to be 'dirty signals' i.e. MAF, MAP, LAMBDA, Some Pressure Sensors or any other analogue sensor which gives off a lot of noise (where the Filtering, and Analogue to Digital Conversion is done inside the ECU) , you can still add more earths using the detachable ground leads on the other 3 channels to try and improve the signal quality, but i must admit this is a rare occassion that the extra grounds are required so one really does do the job the majority of the time hence the blue lead has the fixed ground.