I've always had trouble holding my camera level. No matter how hard I try, my pictures always end up with a slight tilt. This is especially apparent when I shoot panoramas - they always end up skewed one way or another, or with actual sawtooth edges.
To help me, the camera has a grid pattern that I can turn on in the viewfinder and superimpose on the scene I'm viewing. In theory, I can use the lines to line up with the horizon, or with some vertical feature. But it never seems to work. My pictures are still tilted.
So I got a fancy spirit level that goes in the camera's accessory shoe. (Most of my cameras don't have accessory shoes, so it's also wishful thinking on my part.) This didn't work either, since you have to take your eye away from the viewfinder to watch the level. Too bad. Another great idea dies aborning.
Then I got a new smartphone. These things have more sensors than a NASA space probe. Skipping over the GPS, the three-axis accelerometer, and the gyroscope, we come to the one I'm interested in -- the orientation sensor. This sensor measures the tilt in all three axes. It was originally used to see if the phone is vertical or horizontal so the screen layout could be adjusted for the proper viewing. Current versions are far more accurate and precise, thus allowing the phone to be used for its main purpose -- playing video games.
The photos above show a phone app that puts a bubble level on its screen.
Many cameras already have some sort of orientation sensor that's used to tell whether the camera is being held vertically or horizontally. I have no idea whether these are as accurate as the one in my smartphone, but how expensive would it be to add this facility? Even the least expensive smartphones have this now, so the technology is available and relatively low in cost.
Think about pressing a button and having a bubble level show up on your camera's finder. You could call up different versions, depending on the leveling task at hand. Imagine, no more tilted horizons or skewed panoramas.
Once again, camera makers. If my smartphone can do this…
Note: Interestingly, even though smartphones have these nifty attitude sensors, they don't use them to help level the pictures from their own cameras.