trying to figure out the "ata" gauge

[MadBlaster]

Maybe this. The intake manifold is a fixed volume/space. When you increase the throttle in the cockpit, you are mechanically increasing the fuel/air mixture relative to that volume/space of the intake manifold (engine vacume sucks in the air/fuel mix). There must have been a pressure sensor at the intake manifold that reads the fuel/air pressure and feeds the ata gauge its reading.

More air/fuel makes engine cycle faster and must be offset by increased load to keep from over-rpms. Too much fuel/air when the engine is under heavy load means there isn't enough vacume (due to low rpms) to handle the increased fuel/air and the engine lugs.