Definition of position micrometer in English:

position micrometer

noun

rare
  • An apparatus for measuring the position angle of one celestial object relative to another, containing a thread or wire mounted at the common focus of the objective lens and eyepiece of a telescope, which can be rotated in a plane perpendicular to the axis of the telescope; an apparatus similarly used with a microscope.

Origin

Mid 19th century; earliest use found in The Penny Cyclopaedia.