The micrometer is a particularly close-meshed graticule that is brought into the image plane of the objective of a telescope or microscope . Micrometers enable an exact angle or distance measurement and are mainly used in astrometry and microscopy. For astronomical instruments there were simple versions as early as 1700, for microscopes in the 19th century.
Ocular micrometers , on the other hand, have a movable network of threads for measuring fine angles in the field of view of the measuring telescope . The recording micrometer also has a solid thread. With the movable thread the observer continuously drives a star after . In the meantime, electrical contacts trigger an exact time registration , which significantly reduces the reaction time when passing through a star - the so-called personal equation .
Object micrometers are used in microscopy to determine the length of objects.