ah I see fuzzy, it's difficult to do this online at work without beersmith running in front of me to reference. I thought you were talking about something I was unfamiliar with. I also do what it sounds like you do, or something similar. I look at the estimated preboil volume and then I make sure that I collect that exact amount. so in your picture above I would collect 1.79 gallons. if there was still more runnings at that point I simply turn off the valve and stop. that way I know that my volume is always correct and only have to worry about the gravity part of the equation.