Johnson's 40-6648 Self-Leveling Cross & Line Laser combines the features of a cross-line laser with an additional 90 degree plumb line useful for checking square reference of beams, posts, or any other object. A 1/4 In.-20 tripod thread and manual mode also let you project orthogonal lines at any angle, for stairs and other non-level applications. Includes (2) AA alkaline batteries)