Abstract: A support is provided which is arranged to accommodate a plurality of open-ended receptacles such as test tubes. The support includes openings and retainer members which cooperate to frictionally embrace the sides of the tubes so as to permit limited orbital motion of the tubes with respect to the openings. A sensing and leveling assembly beneath the bottoms of the tubes is arranged to cooperate with an arm located above the open ends of the tubes. The sensing and leveling assembly is resilient, such that upon engagement with the bottoms of the tubes they are gently forced against the arm, whereupon the relative positions of the tube bottoms are detected and noted by electronic means. The release of the arm allows the resilience in the sensing and leveling assembly to relax causing the bottoms of the tubes to be raised to a common horizontal plane.