A Short History of
Measurement
Cubit
The ‘Cubit’ was the first recorded
standard linear measurement.
Defined by the distance from the tip
of the forefinger to the middle of the
elbow
Cubit was used by Egyptians for
building pyramids (2750 B.C.)
Mean error in length of sides of
Khufu Pyramid at Gizeh in Eqypt
was 1.5mm
Hand
The Cubit was subdivided into several other
measurements. One hand is measured with
the fingers closed and from end of the
thumb to the other end of the palm
The Height of a horse is still
measured in hands today.
1 hand = 4 inches = 101.6mm
Foot
History believes that the foot was
given its name from the human
body part. The length of a
human foot was measured from
the heel to the tip of the big toe.
From Egyptians through the
Greeks and Romans to present
day the length of one foot has
increased considerably.
This is caused by the use of the
foot in building and as time
developed the use of measuring
with boots on feet has increased
the size of one foot
Today 1 Foot = 12 inches = 304.8 mm
History of the International Systems of Units (SI)
1799 - French Revolution and the subsequent deposition of two platinum
standards representing the meter and the kilogram, on 22 June 1799, in the
Archives de la République in Paris
1832 - Gauss promoted using the Metric System. Gauss was the first to
make absolute measurements of the earth’s magnetic force in terms of a
decimal system based on the three mechanical units millimetre, gram and
second for, respectively, the quantities length, mass and time.
History of the International Systems of Units (SI) cont.
1860 - Maxwell and Thomson
further developed Gauss’s work
through the British Association for
the Advancement of Science
(BAAS). They formulated the
requirement for a coherent system
of units with base units and
derived units.
1874 - BAAS introduced the centimetre-gramsecond (CGS) system, a three-dimensional coherent
unit system based on the three mechanical units
centimetre, gram and second, using prefixes ranging
from micro to mega to express decimal submultiples
and multiples. The following development of physics
as an experimental science was largely based on this
system.
History of the International Systems of Units (SI) cont.
1880s - BAAS added the ohm for electrical
resistance, the volt for electromotive force, and
the ampere for electric current in conjunction with
International Electrical Congress .
May, 20 1875 - After the establishment of the
Meter convention the International Committee
for Weights and Measures (ICPM)
concentrated on the construction of new
prototypes taking the meter and kilogram as the
base units of length and mass.
In 1889 the 1st General Conference on Weights and Measures (CGPM)
sanctioned the international prototypes for the meter and the kilogram.
Together with the astronomical second as unit of time, these units constituted a
three-dimensional mechanical unit system similar to the CGS system, but with
the base units meter, kilogram and second.
History of the International Systems of Units (SI) cont.
1901 – Giovanni Giorgi a very
successful Italian Scientist and
Engineer showed that it is possible
to combine the mechanical units of
this meter–kilogram–second
system with the practical electric
units to form a single coherent fourdimensional system. Giorgi’s
proposal opened the path to a
number of new developments
1921 - Giorgi proposal was thoroughly discussed by the several international
organizations.
1939-1946 The discussions led to the adoption of a four-dimensional system
based on the meter, kilogram, second and ampere, the proposal was approved
in 1946
History of the International Systems of Units (SI) cont.
1954 - The introduction of the ampere, the Kelvin and the candela as base units,
respectively, for electric current, thermodynamic temperature and luminous
intensity.
The ampere is officially defined as “the current in a pair of equally long, parallel,
straight wires 1 meter apart that produces a force of 0.0000002 Newton's
(2 × 10−7 N) between the wires for each meter of their length”
The Kelvin is officially defined as “A temperature scale in which zero occurs at
absolute zero and each degree equals one Kelvin. Water freezes at 273.15 K and boils
at 373.15 K.”
The Candela is officially defined as “A unit of luminous intensity equal to 1/60 of the
luminous intensity per square centimetre of a blackbody radiating at the temperature of
solidification of platinum (2,046°K).”
1960 - The name International System of Units (SI) was given to the system
1971 - the current version of the SI was completed by adding the mole as base
unit for amount of substance, bringing the total number of base units to seven.
The mole is officially defined as “The mass in grams of this amount of a substance,
numerically equal to the molecular weight of the substance.”
SI Units
NPLS Beginners Guide to measurement (2010)
Si Units
Quantity
Unit
Symbol
Length
Metre
m
Mass
Kilogram
kg
Time
Second
s
Area
Squared metre
m2
Solids volume
Cubic metre
m3
Liquid volume
Litre
L=10-3m3
Velocity
Metre per second
m/s
Acceleration
Metre per second squared
(m/s2)
Angle
Radian
rad
Angular velocity
Radian per second
rad/s
Angular acceleration
Radians per second squared
rad/s2
Density
Kilogram per cubic metre
kg/m3
Force
Newton
N = kgm/s2
Moment of force
Newton-metre
Nm
Stress and Pressure
Pascal
Pa = N/m2
Frequency
Hertz
Hz = cycle/s
Impulse
Newton-second
Ns
Work
Joule
J = Nm
Power
Watt
W=j/s
Thermal Conductivity
Watt per metre per degree centigrade
W/mC
Specific heat
Joule per Kilogram per degree centigrade
J/kgC
Convection film coefficient
Watt per metre squared per degree centigrade
W/m2C
Heat Power
Watt
W
Heat Flux (heat generation per area)
Watt per metre squared
W/m2
Examples of modern
measurement tools