Sometimes I replace the 2D panel with a HUD. I don't use the 2D panel very often, and these days most FSX planes don't have 2D panels anyway, so I put a HUD there. It's useful at times, especially during race events while landing in dark and stormy nights. But I noticed that the horizon lines would not stay put ON the horizon. It was very strange. I would position the HUD gauge so that the horizon lines were on the horizon, while the plane was sitting on the runway. But as soon as I started flying, the horizon lines would be either above or below the horizon, depending on my plane's attitude. The "ahhhh!" moment came when I was looking at the 2D panel from Dino Cattaneo's T-45C. He put his HUD there and his HUD stays put, locked on the horizon all the time. I noticed he has several entries for the HUD, with comments such as "conformal at zoom 1.0, aspect ratio 16:9" and "conformal at zoom 0.6, aspect ratio 16:9". You can't just make your HUD gauge any size you want. It has to be "tuned" to the zoom level you are flying at, which, in my case, in the 2D panel, is 1.0. In the attached pic you can see. With my HUD sized correctly at zoom 1.0, going to zoom 1.5 is bad... This seems obvious now, and it makes perfect sense. But until I saw Dino's comments, it didn't "click". Thanks Dino!