Broadly speaking, an anthropometer refers to any
device that is used to measure various dimensions
(such as height and size) of the human body. See
below for a more specific definition. Anthropometers
are used in anthropometry, which is the study of human
body measurements, such as weight, height, and size,
including folds of skin. Basic common every day
examples of anthropometers are scales, rulers, and
measuring tape (e.g., to measure waist size). 
However, there are lesser known devices that have
been used over time such as the craniometer, which
was a metallic device fit around the head to measure
skull size.
An anthropometer
FEATURED BOOK: The Measure of Man and Woman

These devices were once used to measure the association between skull size and
intelligence but now days are used by some dentists to make various measurements of
the face and skull to properly fit a patient for dentures.

Modern technology has led to advanced forms of anthropometers. Perhaps the best
examples are measurement techniques that can be used based in magnetic resonance
imaging (MRI). MRI scans produce extremely detailed pictures of the inside of the body
by using very powerful magnets and computer technology. A good example of applying
MRI to anthropometry is when it is used to measure the volume of the brain, including
specific areas of the brain.
"Where Medical Information is Easy to Understand"™
There are some who define anthropometers as only referring to
devices with measuring marks that consist of a vertical rod
connected to two horizontal arms (only one of which is movable) to
measure the arms, legs, and trunk. Essentially, this definition refers
to a complex type of measuring stick. Examples of measurements
taken with these types of anthropometers are measurements of
shoulder width and bone length. Anthropometers assist doctors in
tracking the development of babies and older children over time.
Anthropometer comes from the Greek word "anthropo" meaning
"human," and the Greek word "metron" meaning "measure." Put the
words together and you have "human measure."