Qooltek Multipurpose Magnetic 2 lines Laser Level Level Vials Adjusted Standard Right-angle Marking Device Hang shelves and cabinets, tiles and picture frames with accuracy. This tool combines Fastening Pin,Magnetic,a two-position bubble level and a laser level into one tool. Magnetic, 5/8" Screw bottom, Back up Battery:3 x AG 13 Button-Cells. Note: Laser Ranging Error,that is given as "0.55" at 30feet". Used widely in civil engineering or construction field.