Micrometer caliper
{Circular micrometer}, or {Ring micrometer}, a metallic ring
fixed in the focus of the object glass of a telescope, and
used to determine differences of right ascension and
declination between stars by observations of the times at
which the stars cross the inner or outer periphery of the
ring.
{Double image micrometer}, a micrometer in which two images
of an object are formed in the field, usually by the two
halves of a bisected lens which are movable along their
line of section by a screw, and distances are determined
by the number of screw revolutions necessary to bring the
points to be measured into optical coincidence. When the
two images are formed by a bisected object glass, it is
called a divided-object-glass micrometer, and when the
instrument is large and equatorially mounted, it is known
as a heliometer.
{Double refraction micrometer}, a species of double image
micrometer, in which the two images are formed by the
double refraction of rock crystal.
{Filar micrometer}, or {Bifilar micrometer}. See under
{Bifilar}.
{Micrometer caliper} or {Micrometer gauge} (Mech.), a caliper
or gauge with a micrometer screw, for measuring dimensions
with great accuracy.
{Micrometer head}, the head of a micrometer screw.
{Micrometer microscope}, a compound microscope combined with
a filar micrometer, used chiefly for reading and
subdividing the divisions of large astronomical and
geodetical instruments.
{Micrometer screw}, a screw with a graduated head used in
some forms of micrometers; turning the head one full
revolution advances the position of the tip of the screw
only by a little.
{Position micrometer}. See under {Position}.
{Scale micrometer}, or {Linear micrometer}, a minute and very delicately graduated scale of equal parts used in the field of a telescope or microscope, for measuring distances by direct comparison. [1913 Webster]