The stock Compass app in iOS 7 comes with a level tool in addition to the compass. To access the level tool, open the Compass app and swipe to the left. It has a simple design that shows the tilt degree with two white bubbles in a black background. Level your iPhone until the two bubbles align, and the screen changes to green when it is levelled. In case you are curious, there is no stock Compass app for the iPad.