The document summarizes the evolution of the metric system from its origins in 1790 France to the proposed 2018 redefinition based on fundamental constants of nature. Key events include the 1793 definition of the meter based on the Earth's circumference, the establishment of the kilogram and international prototype in 1889, and the gradual shift to defining units through physical constants like the speed of light (meter) and Planck's constant (kilogram). The 2018 redefinition aims to define SI units in terms of seven defining constants, bringing the system into closer alignment with the natural world.

1. The Evolution of the Metric System:
from Precious Lumps of Metal to Constants of Nature
Dr Ilya Budovsky
1 November 2018

2. 1790

3. Louis XVI
Jean Baptiste Joseph Delambre Pierre Méchain
1790
Barcelona
Paris
Dunkirk
1793: 1 metre equal to one ten-millionth
of the distance between the North Pole
and the Equator
1795: The kilogram – the mass of one
cubic decimetre of water at the melting
point of ice.

5. A copy of the "provisional" metre
36 rue de Vaugirard, Paris (1796-1797)

6. The National Measurement Institute of Australia (NMI)
NMI is responsible under the National Measurement Act (1960) for Australia’s
top-level infrastructure for physical, chemical, biological and legal measurement.
NMI delivers measurement infrastructure and services to Australia, to:
• Ensure that measurements in Australia can be reliable and fit-for-purpose
• Ensure that measurements made in Australia can be accepted
internationally
• Contribute measurement expertise to national policy development
• Administer Australia’s national trade measurement system (value ~A$750
billion p.a.)
• Support the adoption of measurement technologies in real-world situations
in support of Australian productivity, competitiveness and innovation

7. • Signed on 20 May 1875 by representatives
of seventeen nations. Australia joined in
1947.
• The basis for the international agreement on
units of measurement.
• 20 May is now the World Metrology Day.
The Metre Convention (Convention du Mètre)
59 Member States and 43 Associate States of the Metre Convention

8. The Metre Convention (Convention du Mètre)
The International Committee for Weights
and Measures (CIPM) - 1889
The General Conference on Weights and
Measures (CGPM) - 2014
The International Bureau of Weights and
Measures (BIPM)
Consultative Committees
Barry Inglis

9. ART. 6 (1875)
The International Bureau of Weights and Measures is charged with:
1° all comparisons and verifications of the new prototypes of the metre and the kilogram;
2° the conservation of the international prototypes;
3° the periodic comparisons of national standards with the international prototypes and their
official copies as well as those of the standard thermometers;
4° the comparison of the new prototypes with the fundamental standards of non-metric weights
and measures used in different countries and in the sciences;
ART. 7 (1921)
After the Committee will have carried out the work of coordination of measurements related to electrical
units, and when the General Conference shall have so decided by unanimous vote, the Bureau will be charged
with the establishment and the conservation of standards of electrical units and their official copies as well as
the comparison with these standards of national standards or other precision standards.
The Bureau is also charged with determinations related to physical constants for which more accurate
knowledge might serve to increase the precision and ensure better uniformity in the fields to which the units
mentioned above belong
The Metre Convention (Convention du Mètre)

10. The International Prototype of the Metre - 1889
Creating the metre-alloy in 1874

11. The International Prototype of the Kilogram - 1889

12. Evolution of the SI
cgs (1881?) MKS MKSA SI (1960)

13. From units to constants
J.C. Maxwell (1870)
“If we wish to obtain standards of length, time and mass which shall be
absolutely permanent, we must seek them not in the dimensions, or motion or
the mass of our planet, but in the wavelength, the period of vibration, and
absolute mass of these imperishable and unutterable and perfectly similar
molecules.”
G. Jonstone-Stoney (1881)
“Nature presents us with three such units”
M. Planck (1900)
“It offers a possibility of establishing units of length, mass, time and temperature which
are independent of specific bodies or materials and which necessarily maintain their
meaning for all time and for all civilizations, even those which are extraterrestrial and
nonhuman, constants which therefore can be called fundamental physical units of
measurement”.

14. Quantum effects
An effect that can not be explained by classical physics
(classical mechanics, electrodynamics etc) and requires
quantum mechanics to be explained.
https://www.quora.com/What-is-a-quantum-effect

15. A Brief History of Changes in the SI
• 1948 Decision of 9th CGPM to establish a practical system of units
• 1954 Decision of 10th CGPM on the six base units to be used
• 1960 SI adopted by the 11th CGPM – kg, m, s, A, K, cd
• 1960 metre redefined in terms of Kr 86 radiation 11th CGPM
• 1967 second redefined in terms Cs transition 13th CGPM
• 1971 mole defined as base unit (14th CGPM)
• 1983 metre redefined based on fixed value of c (17th CGPM)
• 1990 Electrical units based on conventional values for 2e/h and h/e2, KJ and RK
• 2018 kg, A, K, mole, redefined; definitions of m, s, cd re-stated (26th CGPM)

16. Why the need to revise, redefine the SI
Enable the technologies of the future
The kilogram – last physical artefact standard, drifting
The electrical units – currently maintained outside of SI
International concern – revision under discussion for many years - resolutions
adopted by last four CGPMs, since 1995
A system based on invariant constants of nature fully meets essential
requirements
Constants are now known experimentally with sufficient accuracy
Long-term stability
Internally self-
consistent
Practically
realisable
Uniform and accessible worldwide

17. The present SI
https://www.bipm.org/en/measurement-units/

18. The Second (1967)
133Cs
6s
electron
F = 3
F = 4
f = 9.192 631 770 GHz
Hyperfine splitting of
the 6s electron level

19. Cesium Clock

20. Dissemination of Australian legal reference units of Time interval, Frequency and Time of day

21. The Metre (1983)
c = 299 792 458 m / s
is defined by fixing the speed of light
l l =
c
f

22. Australian realisation of the Metre
NATA accredited calibration services for:
• Laser interferometers, up to 20 m
• Gauge blocks, 0.5 to 100 mm
• Length bars, 100 to 1300 mm
• Line scales, up to 1 m
• EDM instruments, up to 650 m
Best uncertainty capability: ± 40 nm for laser interferometers

23. The Ampere
I = 1A
1 m
F = 2 x 10-7 N/m
André-Marie Ampère

24. Voltage – the Josephson effect
I V
+
–
f
Voltage(µV)
Current (mA)
V =
h
2e
f
Brian Josephson (1962)

25. Resistance – the Quantum Hall effect
NRC V0054a : 0.32K : 10mA
0
3
6
9
12
15
0 2 4 6 8 10 12
Magnetic Induction (T)Resistance(kW)
I
V+ –
B
RH =
h
e2
Klaus von Klitzing (1980)

26. Current Definitions (continued)
Results of BIPM.EM-K10.b key international comparison of
Josephson Voltage Standards
NMIA
Since 1990 electrical units are based on
conventional values for 2e/h and h/e2, KJ and RK
Australian standard of Voltage Australian standard of
Resistance

27. The kilogram
equals to the mass of a Pt-Ir cylinder housed
at the BIPM in Paris

28. Current Definitions (continued)
candela, cd – in terms of radiated power W or
kg, m, s
kelvin, K – in terms of triple point of water
mole, mol – in terms of numbers of atoms in
0.012 kg of carbon 12
+ 22 derived units

29. The proposed revision
• SI base units: kilogram, kelvin, ampere, mole, second,
metre, candela retained - the same SI not a new system
• Base Units: kilogram, kelvin, ampere, mole to be re-defined
• Base Units: second, metre, candela to be restated in same
format for consistency
• All definitions to be in “explicit-constant” format based on
seven defining constants

30. Seven Defining Fundamental Constants
• Hyperfine splitting frequency of the caesium 133 atom ΔvCs
• Speed of light c
• Planck constant h
• Elementary charge e
• Boltzmann constant k
• Avogadro constant NA
• Luminous efficacy Kcd

31. Proposed New SI definitions

32. Relationship between mass and Planck Constant
• Production and delivery of
electricity and gas
• Efficient use of energy in
buildings, appliances and
transport.
Einstein:
E = mc2Er:
C
Planck:
E = hnergy
Sector:
mc2 = hn
m h
Experimental realisation: Watt Balance
since 2017: Kibble Balance

33. The watt balance renamed
http://www.npl.co.uk/news/in-memory-of-dr-bryan-kibble-1938-2016

34. Kibble balance – weighing phase
Carlos Sanchez, NRC

35. Kibble balance – moving phase
Carlos Sanchez, NRC

36. Original Kibble Balance at NRC Canada

37. The Avogadro Sphere – International Avogadro Consortium and NMI Japan


R
ceM
hN
2
)( 2

A
SI sphere measurements:
• Volume
• Mass
• Atomic spacing
• Molar mass
Achim Leistner at the Australian Centre for
Precision Optics, holding a 1 kg, single-crystal
silicon sphere for the Avogadro project.

38. Proposed New SI definitions (continued)

39. Proposed New SI definitions (continued)

40. Key Conditions to be met before Redefinition
• Consistent values for h from at least 3 independent experiments, including watt-balance and XRCD,
at least one to have an uncertainty not greater than 2x10-8 and agreement within 5x10-8
• Uncertainty of Boltzmann constant k to be < 1x10-6 with agreement between two different methods of
primary thermometry to < 3x10-6
• Mass standards used in the experiments to be compared as directly as possible with the international
prototype
• Procedures for future realisation and dissemination of kg validated
• Mises en pratique in place for all new definitions
• Initiate awareness campaigns to alert user communities

41. Where are we now?

42. Resolution 1. 25th CGPM 2014
encouraged
• continued effort in the NMIs, the BIPM, and academic institutions to obtain data relevant to the
determination of h, e, k, and NA with the requisite uncertainties,
• the NMIs to continue acting through the CCs to discuss and review this data,
• the CIPM, together with its Consultative Committees, the NMIs, the BIPM, and other organizations such
as the International Organization of Legal Metrology (OIML), to complete all work necessary for the
CGPM at its 26th meeting to adopt a resolution that would replace the current SI with the revised SI.

43. Determinations of h and k
CCM criteria
At least 3 experiments,
using 2 different methods
with ur < 5 x 10-8, at least
one with ur <2 x 10-8
from Barry Wood, NRC private communication
from The Boltzmann constant and the
new kelvin White and Fischer, Metrologia 52
(2015) S213–S216
CCT criteria
Value of k with ur< 1 x 10-6
based on two
“fundamentally different”
methods with ur< 1 x 10-6.

44. Realisation of the mass scale

45. Global impact on the revised SI
Underpin future requirements for increases in accuracy
As science and technology advances, the demands for the accuracy of
measurements will continue to increase. The 2018 definitions will enable
these to be met for many years to come.
Facilitate universality of access to the agreed basis for worldwide
measurements
This has been an ambition for the “metric system” that goes back more than
200 years. From 2018 it will be possible to realise all the definitions
universally for the first time.

46. Global impact on the revised SI (continued)
Use the rules of nature to create the rules of measurement
Using the constants in nature allows the scientific and industrial community to
accurately scale their measurements from the smallest to the largest
quantities. It will tie fundamental measurements at the atomic (and quantum)
scales to those at the macroscopic level in areas such as mass and
temperature, where previously it has been done using less accurate indirect
methods.
A springboard for future innovation

47. Impact on the SI base units after redefinition
• second, candela, metre – no change
• kilogram - takes on uncertainty of h
• ampere – negligible uncertainty but a step change of approx. 1 x 10-7
from the present ‘as maintained’ value
• kelvin – Temperature of triple point of water will take on uncertainty of k
• mole will take on uncertainty of NA h

48. Direct Josephson comparisons
1×10−7
1×10−9
Impact of shift in the Ampere

49. From Parks et al, IEEE Trans. Instrum. Meas., June 2013
Set of 4
Zeners used
in North
American
comparison
series
Zener reference drift example
1×10−7
Residuals from fit:

50. Mises en pratique
Mises en pratique, or practical methods for realising the units under the proposed
revised definitions, have been prepared by the relevant Consultative Committees and
are in place or undergoing final revision.
https://www.bipm.org/en/
measurement-units/rev-si/

51. What next?
• All conditions for re-definition have
been met or are well advanced
• On target to present a Resolution
for change to the 26th CGPM, to be
held at the Palais des Congrès de
Versailles on 13 – 16 November
2018
• Proposed date of effect 20 May
2019 (World Metrology Day 2019!)

52. CGPM 26 Open Session on 16 November 2016
https://www.bipm.org/utils/en/pdf/26th-CGPM-open-session.pdf

53. Conclusions
• This is a once on a century event
• It will enable technological progress without disruption to millions of
measurements performed every day
• The proposed re-definitions do not constitute a ‘new’ system (SI)
• All conditions for re-definition have been met or are well advanced
• On target to present a Resolution for change to the 26th CGPM in 2018 (26th
CGPM to be held at the Palais des Congrès de Versailles on 13 – 16
November 2018)
• Proposed date of effect 20 May 2019 (World Metrology Day 2019!)

54. My favourite quotes about measurement
Peter Drucker (1909-2005)
“You can't manage what you can't measure”
Rear Admiral Grace M. Hopper (1906-1992)
“One accurate measurement is worth a thousand expert opinions”
Fred Lehany (1915–1994)
“Metrology is like air ...”

55. The Quantum NMI Logo
The Quantum NMI Logo - Spectral distribution of 43 precisely known
harmonics of 400 Hz generated with Josephson Arbitrary Waveform Synthesiser
Quantum NMI Logo in time domain
NMI scientists with Dr Sam Benz (NIST,
USA)
Dr Ilya Budovsky
Ilya.Budovsky@measurement.gov.au
+61 2 8467 3541