An instrument to determine the radii of curvature of curved 
surfaces such as the surfaces of lenses and mirrors. It 
comprises of a metal frame with 3 pointed legs arranged at 
the corners of an equilateral triangle. The frame is fitted 
with an accurately machined micrometer screw with a brass 
dial head scale 40 mm diameter divided into 100 divisions 
registering on a vertical scale 10-0-10 mm with intervals 
equal to the pitch of the screw. The spherometer is 
available in 0.5 and 1mm pitch.