VisualLevel: From NorthStar Navigation

VisualLevel measures the elevation angle of the center of your iPhone camera. When you start VisualLevel it continuously displays the elevation angle of where your phone’s camera is pointed.

You can also use VisualLevel to measure the height of, or range to, an object. First you aim the crosshairs at the center of your camera at the bottom of the object and press the button in the center of the VisualLevel display. VisualLevel records the elevation of that point. You may then point the camera at the top of the object and record the elevation of the top. Then if you have an estimate of how far away you are from the object VisualLevel will calculate its height. Conversely if you know the height of the object VirtualLevel will allow you to calculate the distance you are from it.