What is Spherometer ?

 A spherometer is used for the measurement of thickness of thin plates and radius of curvature of a spherical surface. It works on the principle of a micrometer screw gauge.

It consists of a metal frame supported on three fixed legs of equal length. The end of three legs are pointed and form the three corners of an equilateral triangle. A screw whose pitch is usually 1mm carries a circular disc ( having a circular divided into 100 equal parts ) at its top, is so supported that the tip of this screw is at the centre of the triangle formed by the tips of the three legs. A small main scale is fixed vertically at one end of the frame very close to circular disc and is usually graduated in millimetres. The reading of the circular scale is taken against the inner edge of main scale.