A micrometer is an instrument for measuring accurately dimensions or separations. Its
basis is that when a screw is turned once, it advances or retreats a
distance equal to its pitch. The hairlines in telescope and microscope eyepieces are adjusted by means of
a precision micrometer screw to measure separations.
|A vernier micrometer
The micrometer caliper has a G-shaped frame on whose
"leg" is a scale; inside the leg runs a screw (of pitch usually 0.5
mm) attached to a thimble, calibrated for fractions of a turn, which
runs over the scale. An object is placed between the screw's spindle
and an anvil at the far side of the G's opening, and the screw turned
until the object is just held.
For greater accuracy (of the order of 1 μm) a vernier
scale may be used.
- A micrometer is also a unit of length, equal to one millionth of a meter (μm). (British
spelling: micrometre.) Known in the CGS system of units as