Three-legged base with precision screw in the center to measure deviation of a (spherical) surface from flatness. Vertical scale (adjustable) calibrated 0-40mm to show approximate position of ventral screw. Plate on central screw calibrated 0-50 for finer measurements. (Screw travels 1 mm in two revolutions.) Three legs are 1" from center, but can be moved to 15 mm (?) from center.
