Use iPhone as a level
Use your iPhone to determine whether an object near you is level, straight, or flat.
Open Measure. (On iPhone 5s, iPhone 6, and iPhone 6 Plus, open Compass instead.)
Tap Level, then hold iPhone against an object, such as a picture frame.
Make an object level: Rotate the object and iPhone until you see green.
Match the slope: Tap the screen to capture the slope of the first object. Hold iPhone against another object and rotate them until the screen turns green.
To reset the level, tap the screen again.