Strong re-enforced frame Fully sealed solid rail (six sided) extension eliminates flex and deflection for smooth movement Removable 1 5/8" stand-offs reach around braces Top horizontal vial is permanently positioned at eye level Printed scale on slide extension allows the level to be pre-set and locked to the correct wall height Vials are guaranteed for life never to fog, leak or require adjustment One Horizontal (level) and two Vertical (plumb) vials