A spirit level, bubble level or simply a level is an instrument designed to indicate whether a surface is horizontal (level) or vertical (plumb). Different types of bubble levels may be used by carpenters, stonemasons, bricklayers, other building trades workers, surveyors, millwrights and other metalworkers, and in some photographic or videographic work. Hold any of the phone's four sides against an object to test it for level or plumb, or lay it down on a flat surface for a 360Ã??Ã?Â° level. No permission required at all? No ads? Calibrate any side independently? Calibrate relatively (another object surface) or absolutely (earth gravity)? Show angle in degree, inclination in percent, roof pitch or inches per foot (:12)? Sound effects to calibrate without looking at the phone? Install on SD? Orientation locking.