6′ to 10′. Strong re-enforced frame. Fully sealed solid rail (6 sided) extension eliminates deflection, and delivers the smoothest extension movement available. Removable 1-5/8″ stand-offs reach around braces. Top plumb vial is permanently positioned at eye level. Frame side opposite the stand-offs is a level measuring surface and straight edge. Vials are guaranteed for life never to fog, leak, or require adjustment. Certified accuracy in the top read position: 1/32″ over 72″.