https://imgur.com/a/snDUsSn I'm a first time home owner, and I'm trying to figure out how these dampers work. The above link are the pictures to my two ducts (2nd floor and main floor/basement). I know that when the lever is parallel to the airflow, the duct is supposed to be open, and when it's perpendicular, it's closed. My question is how this applies to an elbow duct where both lever positions are simultaneously parallel and perpendicular to airflow. Is A open or B open? I can picture the inside of the duct when it's straight, but I don't know how the damper is installed on an elbow like this. As for the two bottom pictures (straight duct), neither position A nor B are parallel nor perpendicular. Position A is pointing at a 7:30 position, and B is pointing at 9:30. Is it supposed to be like this? Which one is open and which one is closed? My final question is why am I not feeling the effect when I open or close these ducts? I've tried multiple configurations and when I put my hand next to the vents either at the main floor or 2nd floor, I can't tell the difference in air pressure. Is there a device that I can buy to test the air that's being pushed out of the vents? Thank you in advance!