I saw a guy using a dial a charge, charging cylinder. I do alot of critically charged stuff, so I bought one. How do I fill this thing, the instructions tell how, but it leaves a few open questions like do I need to pull a vacuum on it first or no. I bought it used, but it still appears new. I called Robinair who makes it, and they told me if I can, to do it, well im thinkin why couldnt I? And also if I dont pull a vacuum on it, wont that put air in my system upon charging it, or am I missing something in the way it works. Then after I empty the cylinder of its refrigerant, will I have to pull a vacuum on it again to use it a second time? Im a little confused on it, as I have only ever used my digital scale, but am sorta eager to use this device I now have. And one last question hypathetically, if I fill it to like say 8 oz, and then I turn on the heater in it, it expands to 10oz now, would I put the full amount in the my system if I needed 8oz of refrigerant even though it now says ten, or would I put still only 8 in and stop the filling with two left in the cylinder. This is sorta confusing me. Im guessing all of the charge in the cylinder because even though the volume increased it was still only 8 from the start RIGHT?