A spherometer is a precision physics laboratory equipment or instrument used to measure the radius of curvature of spherical surfaces:

It consists of a central screw and three outer legs forming a tripod, which rest on the curved surface. Additionally, the central screw moves vertically and has a circular scale for accurate readings.
The height difference between the central leg and the outer legs helps calculate the radius of curvature using a standard formula.
It is commonly used in optics labs to determine the curvature of lenses and mirrors, helping ensure proper image formation.