It is the degree to which the measured
value of the quality characteristic
agree with the true value.
The difference between the true value
and the measured value is known as
error of measurement.
Calibration is the process of establishing the
relationship between a measuring device and
the units of measure.
This is done by comparing a device or the
output of an instrument to a standard having
known measurement characteristics.
Calibration is the process of configuring an instrument to provide a
result for a sample within an acceptable range.
Eliminating or minimizing factors that cause inaccurate
measurements is a fundamental aspect of instrumentation design.
The results are used to establish a relationship between the
measurement technique used by the instrument and the known
The instrument can then provide more accurate results when
samples of unknown values are tested in the normal usage of the
A YARD is a unit of length in several different
systems, including English units, Imperial units, and
United States customary units.
It is equal to 3 feet or 36 inches, although its length in
SI units varied slightly from system to system.
The most commonly used yard today is the
international yard, which is equal to precisely 0.9144
The meter is the length of the path travelled by light in vacuum during a time
interval of 1/299 792 458 of a second.
International Prototype meter is defined as the straight line distance, at 0’c
between the engraved lines of a platinum iridium alloy of 1020 mm of total
length and having a cross-section as shown in the figure.
The graduations are on the upper surface of the web, which coincides with the
neutral axis of the section.
The sectional shape gives better rigidity for the amount of metal involved and is
therefore economic in use for an expensive metal.
The metre or meter is the basic unit of length in the International
System of Units (SI).
The metre was defined by the French Academy of Sciences as the
length between two marks on a platinum-iridium bar, which was
designed to represent one ten-millionth of the distance from the
Equator to the North Pole through Paris.
In 1983, the metre was redefined as the distance travelled by light in
free space in 1⁄299,792,458 of a second.
Scale can be accurately embalmed, but the engraved lines posses thickness
and it is not possible to accurately measure.
Scale is used over a wide range.
Scale markings are subjected to wear. However the ends are subjected to
wear and this leads to undersize measurements.
Scale does not posses built in datum. Therefore it is not possible to align the
scale with the axis of measurement.
Scales are subjected to parallax errors.
Assistance of magnifying glass or microscope is required.
Highly accurate and used for measurement of closed tolerances in precision
engineering as well as standard laboratories, tool rooms, inspection
They require more time for measurement and measure only one dimension.
They wear at their measuring faces
They are not subjected to parallax error.
Not a material standard and hence it is not influenced by effects of variation
of environmental conditions like temperature, pressure
It need not be preserved or stored under security and thus there is not fear of
It is subjected to destruction by wear and tear.
It gives the unit of length which can be produced consistently at all times.
The standard facility can be easily available in all standard laboratories and
Can be used for making comparative measurements of very high accuracy.