I don't put the gauge on til I have purged the system. And my OEM said residual CO2 pressure would not affect the reading.One of the first things I asked when I bought my gauge. Guess I got one that can do CO2 as it is not the "typical sort" as you described.
That being said, I am at a loss to reconcile what you are telling me.
Perhaps you could expand a bit into the physics of it. Might make a difference.
What gauge did you buy? Or are you using the smans?
Gotta have the right tool for the job!
Where is all the stuff MADE IN THE USA?
"Thats what we do Troy. Incredible, Invisible, Imbelivable things. We are an Unseen, Unknown, Unvincible fraternity of craftsman.."