Glo-View vial enhances readability in low light. Natural light or hand-held light sources re-charge the vial surrounds. Powerful GripTight rare earth magnets hold to ferrous metal surfaces. Super strong 9 In. solid aluminum frame is job site tough. V-groove frame fits on pipe and conduit. SurroundView vials reflect ambient light for easy-read. Three vials read plumb, level, and 45 degrees. Top-read window for easy viewing.