Sonar Ruler, as it's name might imply, is an app that allows you to measure distances using "sonar" pings. It works similar to how bats find their way around - by making little clicks and listening for the echoes that return. Sonar Ruler takes into account such stuff as the air temperate (since the speed of sound varies) and lets you pick the units (inches, feet, meters). It even lets you edit some of the sonar settings, if you're into that sort of thing. And it has a built in 'level' meter, using the accelerometer (what ruler would be complete without it?). In terms of presentation, Sonar Ruler gets an A+ - the interface looks super cool and it even has a little tutorial movie you can view the first time you run the application (recommended viewing). The sonar view, which I can only assume is the impulse response of the sound, takes up most of the UI, as it should since it looks awesome. You can zoom in and out using gestures and scroll it naturally. My only fault with the UI is that the buttons are a bit thin and the first slider on the 'custom settings' page was really hard to click for some reason.