When running through the effects loop on my VHT the tuner fluctuates much more than plugging the guitar straight into the analog input (seemed dead on that way). I expect it's that way through most effects loops (depending on what's in between)?
G-Major unit flucuates less in the effects loop but still isn't as accurate as the Eclipse, just easier to read. The GuitarRig3 tuner seems not quite as presice as the Eclipse either. I need to investigate that more.
