YES, at .02 is the DRAFT of the STOVE, or INCHES OF WATER COLUMN (Draft).
So, at .02 that means LESS DRAFT on the stove, MORE heat in the stove, less up the chimney. Since, now the BARO is OPEN, it is pulling the extra draft from the room.
.08 MORE Draft out of the stove, less heat in the stove, Baro Closed down more, Less draft from the room.
it's the chimney effect. It has to draw the air from either the ROOM or the STOVE. basically a combination of both.
Say Your Chimney with NOTHING hooked to it draws .10 on the draft gauge. Now without the Baro, it would be drawing .10 from your stove.
Next, you put the baro in and set it to .04, it draws .04 from the stove and .06 from the room to equal the .10 total that we see above.