Hear a beep when you hold the iPhone up to something, like a reverse-park sensor the beeps get quicker depending on how level (or vertical) the surface is.
You can hold any side of the iPhone against any surface, and instantly the beeps will tell you if it is level. Using the iPhone against a wall will automatically display the 3D plumbline, but when you hold it against a surface like a shelf, a standard bubble level is shown.
The advanced calibration and geometry calculations make this the most accurate bubble level in the App Store.
Cool - ★★★★★ - Very useful app
Really easy to use - ★★★★ - Calibrating this level is easy and gives accurate results.
* Bubble Level *
An easy-to-use spirit level. Simply hold the iPhone up to the surface you want to measure, and the large, clear display shows how level the surface is. You can use the iPhone either face-up or on it's side.
* Plumb Line *
Based on the traditional tool used for centuries, the plumb line is used to test if something is vertical. Hold the back or edge of the iPhone against the surface, and watch the plumb-line swing to position objects perfectly vertical.
* Sound *
Just like a reverse-park sensor, the app makes a sound that becomes quicker as it gets closer to level. The audio signal allows you to accurately level objects even when you can't see the front of the phone. Choose from 6 different sounds, and different sensitivity settings.
* Sharing *
Post to Twitter, Facebook and email. You can also upload photos to Facebook and Twitter (using Twitpic) and attach photos to emails.
For people who like dual level and bubble level apps.