STABILA levels are unparalleled with regard to their accuracy and dependability. The secret - the vials made of block acrylic glass are firmly epoxy-locked in the frame. A perfect system. The vial is firmly cast in the high strength aluminum frame with non-shrink epoxy. No re-adjustment, no realignment, no tensioning against springs made of steel or fatigued plastic, no welding or clamping stresses. Just as accurate after 10 years as on the first day..