Blank PIDs/PIDs always zero

[turbo5.3silverado]

Hi,
I am new to HP tuners and have a question about PIDs. On my 2010 silverado i am trying to log knock retard so I can see where it is under boost? I have tried knock retard and total retard but both are always zero or not responding on the scanner? I Know I,m missing something as I can see the knock retard on my scan tool? any ideas would be greatly appreciated. thanks

[07GTS]

make sure u have added the pids u want to see in the channels list, press the gear with green + and it will only show available pids to log that u can add to channels

[chevota]

I'm new too and quickly discovered that just because the PID is there and available does not mean it'll do anything. So when in question I load all the ones I think should work, then look for those that actually do something and delete the rest.
Mine does knock for each cyl and I wanted it in a vertical bar gauge so I had to make math to average them; Tools/Math