Read the directions first, filling it is very touchy, I overflowed mine a couple times and had to dump some out. YOu should mount it and level it first! Then adjust the zero knob out 3 full turns, then slowly put some fluid in it until it just gets to zero, then you can use the knob to adjust up or down. Then Hook up the one tube to your chimney.
I have one side hooked to the chimney below the Baro damper coming out of the stove, and the other just open to nothing.
Here is what it should look like and the settings of .02-.04 Marked (Higher is good draft Farther To the right), you don't want too much draft, you will be wasting heat up the chimney. It doesn't vary much.
Mine varies around .03 to .05, the baro damper works to maintain the .04 settings. It starts to open around .04.