The Probert Encyclopaedia of Science & Technology

MICROMETER

A micrometer is an instrument for measuring minute lengths or angles with great accuracy; different types of micrometer are used in astronomical and engineering work.
The type of micrometer used in astronomy consists of two fine wires, one fixed and the other movable, placed in the focal plane of a telescope; the movable wire is fixed on a sliding plate and can be positioned parallel to the other until the object appears between the wires. The movement is then indicated by a scale on the adjusting screw.
The micrometer calliper, of great value in engineering, has its adjustment effected by an extremely accurate fine-pitch screw (called a vernier).
Research Micrometer