Sphero Meters are small precision instruments for measuring the radius of curvature of spherical surfaces. They can also be used to measure the thickness of a thin plate. A spherometer works on the principle of the micrometer screw. Spherometer consists of a metallic tripod framework supported on three fixed legs of equal lengths. A screw passes through the centre of the tripod frame, parallel to the three legs. A large circular disc graduated with 100 equal parts is attached to the top of the screw. A small vertical scale known as the Pitch scale (P) with the scale reading divided into millimeters is fixed at one end of the tripod frame.
This video explains how to determine (a) the thickness of a glass plate and (b) the radius of curvature of a given spherical surface using a spherometer.