Measuring Up

  Last updated July 11, 2017 at 12:37 pm

Topics:  

This Saturday, 20 May 2017, is World Metrology Day. Get the measure of things.


Never heard of World Metrology Day? Don’t worry, I was doing a PhD in metrology for three years before I found out we had a day for it. So what is metrology, and why does it deserve its own day?


Given how unfamiliar the term is, you could be forgiven for assuming metrology is a very niche discipline, but like electricity generation or the internet, it is an essential part of our modern civilisation. Metrology is the science of measurement, not to be confused with meteorology, the study of the weather. I understand the confusion though, and am getting used to people asking me whether it’s going to rain tomorrow.


It is concerned with the definition of internationally accepted units of measurement (kilogram, metre, etc), the practical realisation of these measurements (that is, how to actually make the measurement), and the traceability of measurements (linking a measurement you make back to a reference in a laboratory).


Image: My metrology laboratory where I work on the transmission of atomic clock signals, author supplied


Every country has a metrology institute. In Australia we have the National Measurement Institute (NMI), the UK has the National Physical Laboratory (NPL), and in the US it’s the National Institute of Standards and Technology (NIST). These institutes are responsible for the scientific, industrial, and legal aspects of measurement.


Scientific metrology focuses on the definition of the units we use to measure things, how to actually make measurements, and how to do it with ever higher degrees of accuracy and precision.


Industrial metrology is concerned with measurement in manufacturing and other technical applications such as the calibration of machinery. Industrial metrology is so important to a nation’s development that the condition of its industrial metrology program is a key indicator of a country’s economic status.


Legal metrology is about the statutory requirements of measurement for trade, taxation, and public safety. Whenever you weigh bananas at the supermarket, buy petrol, or check the time, those weights and measures are strictly legally controlled.


World Metrology Day is an international event commemorating the signing of the Metre Convention on 20 May 1875. 17 nations signed a treaty for the purpose of coordinating worldwide uniformity of measurement and the development of what we now call the metric system and the International System of Units (SI).


Metrology institutes around the world take the opportunity to celebrate and communicate the importance of metrology in our modern world. In Australia, which joined the treaty in 1947, the NMI commemorates the occasion by presenting two awards for outstanding achievement in measurement. The USA is also a signatory of the treaty, meaning that, legally speaking, America uses the metric system. Someone should probably tell them.


The measure of things


Right now is an exciting time to be a metrologist. Two big developments currently taking place in metrology involve the redefinition of two of the most basic units of measurement we use every day. The kilogram and the second.


The SI system has seven basic units of measurement, which are:



  • the metre for length,

  • the kilogram for mass,

  • the second for time,

  • the ampere for electric current,

  • the Kelvin for temperature,

  • the mole for amount of substance (in terms of number of atoms or molecules), and

  • the candela for intensity of light.


All other measurements, such as volts or kilowatts, are derived from these basic units.


The second is currently defined as “the duration of 9,192,631,770 periods of the radiation corresponding to the transition between two hyperfine levels of the ground state of the caesium-133 atom”. In less technical terms, in an atomic clock, carefully controlled atoms of caesium-133 will emit microwaves with a frequency of 9,192,631,770 Hz (the clock will “tick” at 9,192,631,770 cycles per second), so adding up 9,192,631,770 of these ticks gives us one second.


Metrologists around the world have worked to produce ever more stable and precise atomic clocks. In the last few years, clocks that use atoms of ytterbium have surpassed the caesium clocks we currently use to define the second. In the next few years, we could see the second no longer defined by the over 9 billion ticks per second of caesium clocks, and instead by the 518 trillion ticks per second of ytterbium clocks. It sounds like an insignificant change, and hopefully your boss isn’t going to get angry if you’re a few trillionths of a second late to work, but more precise clocks counting more precise seconds are an important tool for scientific and industrial progress into the latter half of the 21st century.




Atomic clock at NIST. Source: NIST/Wikimedia


The second, and most of the other SI base units, are defined using physical constants, values that are fundamental properties of the universe. While a “second” is a human invention, caesium will emit microwaves at 9,192,631,770 Hz whether it is on Earth or on an alien planet in a galaxy far, far away. The metre is defined by the speed of light, another fundamental property of the universe, which is 299,792,458 metres per second.


But one of the base units, the kilogram, is not defined in terms of fundamental universal constants. The kilogram remains the only unit defined by a physical object, a platinum-iridium ingot called the international prototype kilogram (IPK) stored in a secure vault in France.


Each member nation of the Metre Convention possesses one or more copies of the IPK (Australia has copies 44 and 87). Twice since their production the copies have been re-united in France and weighed, and the results were shocking. The kilogram copies have all changed in mass, and by different amounts. Even the IPK’s six sisters, copies stored next to it in the same vault, disagree with the IPK. This has spurred metrologists to invent a new definition of the kilogram, a definition in terms of physical constants that can be measured accurately by any metrology laboratory in the world, without the need to refer to a physical object on the other side of the globe.


NIST’s copy of the kilogram. Source: NIST/Wikimedia


One possible redefinition of the kilogram is being investigated by CSIRO and involves manufacturing an extremely precise sphere of silicon and counting the atoms in it. Thanks to the computer industry, the technology to produce defect-free, ultra-pure crystals of silicon is readily available. An ingot of pure silicon is cut and machined into a sphere. Special measurement techniques allow the sphere to be polished to size to an accuracy of only one layer of atoms. Mass spectrometry and X-ray measurements allow the spacing between silicon atoms to be measured and so the number of atoms in the silicon sphere to be calculated. The kilogram could then be defined in terms of the number of atoms in an object that could be reproduced by metrology laboratories from a set of instructions.


CSIRO’s prototype silicon sphere is one of the most precisely round objects in the world. If the 93.6 mm sphere was blown-up to the size of the Earth, the tallest mountain on that globe would be less than three metres high.


CSIRO’s silicon sphere. Source: CSIRO/Wikimedia


However, the current front-runner in the race to redefine the kilogram is the Watt balance. The basic design of the Watt balance resembles an old fashioned set of weighing scales, with a mass on one side, and an electromagnet on the other. The electrical power (number of Watts) necessary to balance the weight can be measured very precisely, giving the mass of the kilogram in terms of amperes and volts, something that any metrology laboratory can reproduce.


You can even have a go at building a Watt balance yourself. The US NIST released plans for a desktop DIY Watt balance you can build out of LEGO. It’s about a million times less precise than NIST’s original Watt balance, but if you build it well, it will out-perform your digital kitchen scales.



Who knows, within the next few years, the bananas you buy at the supermarket could be weighed in terms of the “electric” kilogram.


So, this World Metrology Day, take a moment to reflect on how much accurate measurement affects your life, and wonder how many amps and volts the banana you had with breakfast weighs. Dig out your old LEGO sets and find out by building a Watt balance, or just grab a ruler and measure how long it is. Get the measure of things this World Metrology Day.


Want to know more?


Here are some great educational videos about metrology:



Both NIST and NPL have YouTube channels where you can learn more about their current research or the history of metrology.



Did you like this blog? Follow us on FacebookTwitter and Instagram to get all the latest science. 




About the Author

David Gozzard
David Gozzard is a Postdoctoral Fellow in the Department of Quantum Science at the Australian National University where he works on developing laser systems for communications and sensing. David also teaches physics and is a keen science communicator. At the 2017 WA Premier's Science Awards he was named Student Scientist of the Year. Twitter: @DRG_physics

Published By

Science and technology is as much a part of our cultural fabric as art, music, theatre and literature. They play a significant role in our daily lives, yet, in a world dependent on science, we often take them for granted. Australia’s Science Channel believes every citizen has a right, and a responsibility, to be informed, and our mission is to create programs to bring that about.


Featured Videos

Placeholder
Columbia: NASA blew it
Placeholder
The Face of a Stranger
Placeholder
Where Does Space Begin?
Placeholder
The Rarest Drug on Earth
Placeholder
Why is blue so rare in nature
Placeholder
Ant Sisters
Placeholder
Jeremy the Lefty Snail and Other Asymmetrical Animals
Placeholder
Tracking Snow
Placeholder
Smart Slime?
Placeholder
Good in the machine
Placeholder
Kessler Syndrome: What happens when satellites collide?
Placeholder
Why This Skateboarding Trick Should Be Impossible
Placeholder
Charles Camarda on becoming an astronaut
Placeholder
Alan Duffy on what it took to get humans to the Moon
Placeholder
Do aliens exist? Brian Cox explains
Placeholder
From Apollo to Pulsars: Parkes still dishing out the discoveries
Placeholder
Brian Cox on black holes
Placeholder
Australia's 60,000 years of space history
Placeholder
In Class With… Jane Goodall
Placeholder
Etienne Rastoin-Laplane - What's fishy about the Galapagos?
Placeholder
Kit Prendergast - Flowers to keep native bees buzzing
Placeholder
Rebecca Wellard - Eavesdropping on killer whales
Placeholder
Hossein Tavassoli - Mending broken hearts
Placeholder
Dilan Seckiner - Forensic gait analysis
Placeholder
Samuel Bladwell - A new spin on electronics
Placeholder
Sathana Dushyanthen - The double-edged cancer sword
Placeholder
Dwan Price - Nuts and Guts
Placeholder
Catriona Nguyen-Robertson - Exercise takes your immune system for a ride
Placeholder
Thimo Ruethers - The deadly danger of crocs on a plate
Placeholder
Amanda Tauber - Slamming the brakes on metastatic cancer
Placeholder
Hayley Teasdale – The ball that prevents falls (FameLab Australia 2019 Runner-up)
Placeholder
In the Shadow of a Black Hole
Placeholder
In Class With... Monica Gagliano
Placeholder
In Class With... Brian Cox
Placeholder
Start your FameLab 2019 journey now
Placeholder
Nural Cokcetin - It all starts with FameLab
Placeholder
Erinn Fagan-Jeffries - It all starts with FameLab
Placeholder
Ronald Yu - It all starts with FameLab
Placeholder
Noushin Nasiri - It all starts with FameLab
Placeholder
Grassroots
Placeholder
What is machine learning?
Placeholder
Mythbusting artificial intelligence with expert Anton van den Hengel
Placeholder
Using machine learning to predict medical outcomes
Placeholder
KCLOC
Placeholder
Nature Calls
Placeholder
Mexican Fishing Bats
Placeholder
Bittersweet
Placeholder
Timelapse
Placeholder
Invisible Blanket
Placeholder
Look
Placeholder
The Anomalies: Venom Race
Placeholder
Science Meets Making
Placeholder
Spiral
Placeholder
Looking Out There
Placeholder
Protectors of the Penguins
Placeholder
Astroturf
Placeholder
Virtual Humans
Placeholder
Rancheros del Jaguar
Placeholder
Searching For Dark Matter
Placeholder
Finding prehistoric mega-shark fossils on Victoria's coast
Placeholder
The Grandfather of computers
Placeholder
James Cameron talks science
Placeholder
In Class With.....David Suzuki - The Environment
Placeholder
In Class With.....David Suzuki - Career
Placeholder
Sustainable water use with Doug Green
Placeholder
Why is Indigenous science important?
Placeholder
Vanessa Pirotta - Using drones to collect whale snot (FameLab Australia 2018 Winner)
Placeholder
Toby Hendy - Poking Plants (FameLab Australia 2018 Runner-Up)
Placeholder
Muthu Vignesh Vellayappan - Groovy Patches (FameLab Australia 2018 Audience Choice)
Placeholder
Taryn Laubenstein - The Tail of Two Fishes
Placeholder
Richard Charlesworth - Coeliac disease diagnosis can be a pain in the posterior
Placeholder
Pegah Maasoumi - Solar Windows
Placeholder
James Wong - Breathing while you hop: How do kangaroos do it?
Placeholder
Ben McAllister - The ORGAN Experiment: Shining a light on dark matter
Placeholder
Mortaza Rezae - Empowering beautiful minds
Placeholder
Zane Stromberga - Can allergy drugs beat bladder disease?
Placeholder
Working In.....Art - Astrophotography
Placeholder
What's the best way to move - springs or muscles?
Placeholder
FameLab Australia Semi-Final Highlights
Placeholder
Saving lives with platypus milk
Placeholder
Australian astronomers witness death throes of a cocooned star
Placeholder
How Australia's politicians see our future in space
Placeholder
Keeping satellites in the loop
Placeholder
Tim Flannery talks about COP
Placeholder
Tim Jarvis & Tim Flannery talk Climate Change
Placeholder
Andy's Week in Science - robo baby, university rankings, and cancer on circadian rhythms
Placeholder
From chocolate factory to surgery - the milliDelta robot
Placeholder
Andy's Week in Science: video games, low tech transition windows and a new CRISPR technique
Placeholder
Science lessons useful in Art Restoration career
Placeholder
Are drones the future of racing?
Placeholder
The future of esports according to the experts
Placeholder
Seeing is believing with artist Eugenie Lee
Placeholder
The human impact of Art Science collaboration
Placeholder
Follow your Interests in Robotics
Placeholder
Zoz on 3D Printing
Placeholder
Flavia Tata Nardini on women in engineering
Placeholder
Flavia Tata Nardini on the future of the internet
Placeholder
Explore the ocean floor and Antarctic biodiversity
Placeholder
Follow your interests in Medical Research
Placeholder
Artists on Science
Placeholder
What is Space Archaeology?
Placeholder
Follow your Interests
Placeholder
Scientists on Art
Placeholder
3D Printing in Medical Research
Placeholder
Ethical Issues
Placeholder
Problem Solving - Robotics at Dermatec
Placeholder
Problem Solving with CSI
Placeholder
Tamarah King - Earthquake Geologist
Placeholder
True or False with Bajo and Rad BONUS ROUND
Placeholder
True or False with Bajo & Rad
Placeholder
Andy's Week in Science - Cats vs Dogs
Placeholder
FameLab 2018 - Get Involved!
Placeholder
Nural Cokcetin - How FameLab changed my life
Placeholder
Erinn Fagan-Jeffries - How FameLab changed my life
Placeholder
Noushin Nasiri - How FameLab changed my life
Placeholder
Ronald Yu - How FameLab changed my life
Placeholder
Alan Duffy's Top 5 Science Communication Tips
Placeholder
A Judge's Top Tips for FameLab Australia
Placeholder
Brain Candy - Why, Why, Why Michael Stevens?
Placeholder
The Past, Present, and Future of Malaria
Placeholder
This is a video of poo pills being made!
Placeholder
Mind Games - Sports Psychology
Placeholder
Fuel to Win - Sports Nutrition
Placeholder
Fifty years since Australia beat the world to space
Placeholder
ECR Network: Talk Your Science with Alan Duffy
Placeholder
Andy's Week in Science - chimps, klompen, and clouds
Placeholder
Our robot medicine future - heart huggers and micro biohybrids
Placeholder
Six Awkward Cancer Questions
Placeholder
How do you tell if a whale is left-handed?
Placeholder
She Flies - Turning Girls into Drone Pilots
Placeholder
Andy's Week in Science - Magnetic Fabric, Cancer Treatments, and Echolocation
Placeholder
The Science of Sexuality
Placeholder
Sailing Through Space with Bill Nye
Placeholder
Using Sports Science to Help Olympic Athletes
Placeholder
Three and a Half Minutes of Top Shelf Career Advice
Placeholder
New Space Tech with Andrea Boyd
Placeholder
Kelly Meets the Mars Curiosity Rover
Placeholder
Hearts, Opera, and Tough Conversations - Andy's Week in Science
Placeholder
Bill Nye on Science, Girls, and Saving the World!
Placeholder
2017 Prime Minister's Prizes for Science Part 2
Placeholder
2017 Prime Minister's Prizes for Science Part 1
Placeholder
Who Decides the Law in Space?
Placeholder
Scientists Watch Collision That Created Gravitational Waves
Placeholder
Getting Cold Feet Leads to a Whole New Career
Placeholder
ECR Network - Why Every Scientist Should Be on Twitter - The Benefits
Placeholder
ECR Network - Why Every Scientist Should Be On Twitter - The Fears
Placeholder
Live Podcast - Life Vs Science
Placeholder
Origami Robots, Babies, and Kidneys - Andy's Week in Science
Placeholder
Namira Salim and the Zero-G Peace Summit
Placeholder
Elon Musk's Mars Plan: Expert Analysis
Placeholder
SPACE AF - Thursday
Placeholder
My Time in Space
Placeholder
IAC TV Daily Broadcast - Wednesday
Placeholder
SPACE AF - Wednesday
Placeholder
IAC TV Daily broadcast - Tuesday
Placeholder
SPACE AF - Tuesday
Placeholder
IAC TV daily broadcast - Monday
01:00:41
Placeholder
SPACE AF - Monday
Placeholder
Live from IAC 2017
Placeholder
Brew Ha Ha - Technology Rewrites History
Placeholder
Methamphetamine - Gateway Drug to Parkinson's Disease
Placeholder
Concussion, 3D BioPrinting, and The Universe - Andy's Week in Science
Placeholder
Pulsars, Clearwigs, and Pacemakers - Andy's Week in Science
Placeholder
Revolutions - The Quest to Transform HPV Racing
Placeholder
Brew Ha Ha - Hurricane Irma Blows Away Tesla's Rip Off
Placeholder
Brew Ha Ha - The Limit of Your Lifespan
Placeholder
The Recipient
Placeholder
Think Like a Scientist: Natural Selection in an Outbreak
Placeholder
The End of Snow
Placeholder
The Next Rembrandt
Placeholder
The Discarded
Placeholder
The Spectators
Placeholder
Test Tube Babes
Placeholder
Pangolins in Peril- A Story of Rare Scales
Placeholder
Rock Art Project
Placeholder
Pork.0
Placeholder
OWSIA (Darkened Water)
Placeholder
Nex
Placeholder
Northern Quolls
Placeholder
Dish Life
Placeholder
At Street Level
Placeholder
Custom Love
Placeholder
Adrift
Placeholder
A Story from Space
Placeholder
Brew Ha Ha - The Most Dangerous Thing in Boxing May Be the Gloves
Placeholder
ECR Network 2017 – Get Interdisciplinary!
01:27:00
Placeholder
Chris Hadfield: The Future of Space Exploration
Placeholder
Chris Hadfield: Life After Space
Placeholder
Chris Hadfield: Life in Space
Placeholder
Brew Ha Ha - Let's Make Algae Australian of the Year
Placeholder
Brew Ha Ha - Australia's Energy Showdown
Placeholder
Nine Awkward Astrophysicist Questions
Placeholder
Brew Ha Ha - There's No Such Thing as an Exercise Pill
Placeholder
National Science Week Awards Show
Placeholder
Brew Ha Ha - Your 5 Step Asteroid Success Plan
Placeholder
National Science Week Forecast
Placeholder
Open Doors. Open Future. Open Day.
Placeholder
Brew Ha Ha - Lose a Little to Gain Millions
Placeholder
Brew Ha Ha - Crowd Sourcing Origami Astronaut Protection
Placeholder
Brew Ha Ha - T-Rex's Prehistoric Power Walk
Placeholder
True or False with Kale Brock
Placeholder
The Grandfather Paradox
Placeholder
Brew Ha Ha - The Hidden Heroes Tackling Mozzies
Placeholder
Brew Ha Ha - Emergency AI Assistance
Placeholder
Brew Ha Ha - Frogs Forever, Dinosaurs Never!
Placeholder
Brew Ha Ha - Australia, Let's Go To Space
Placeholder
Brew Ha Ha - Welcome to the Microbiome, Archaea!
Placeholder
Brew Ha Ha - Roos Blindside Driverless Cars
Placeholder
Biodiversity of Antarctica Under Threat From Increase In Ice-Free Areas
Placeholder
Brew Ha Ha - The Future of the Census
Placeholder
Tell Me! Brian Cox
Placeholder
Crash, Burn, Tweak, Repeat
Placeholder
Brew Ha Ha - Humans Just Got Older and Wiser
Placeholder
Brew Ha Ha - Cheers to Brain Health?
Placeholder
Gene Therapy Could Cure Allergies
Placeholder
Brew Ha Ha - iHeart Hacking
Placeholder
Ridiculology - New Hubble
Placeholder
Brew Ha Ha - Trees Alone Can't Save Us
Placeholder
Brew Ha Ha - Earth's Accidental Force Field
Placeholder
Dinosaurs on the Big Screen
Placeholder
Brew Ha Ha - Farewell MP3
Placeholder
Kids Beat Grown-ups on Pneumonia Vaccines
Placeholder
Brew Ha Ha - The Booger Conspiracy
Placeholder
FameLab 2017 National Final - Part 2
Placeholder
FameLab 2017 National Final - Part 1
Placeholder
2017 Budget Response
Placeholder
What Are Animal Weapons?
Placeholder
If You Love Both Art and Science, Be a Scientific Illustrator
Placeholder
Getting Personal With Skinks
Placeholder
Brew Ha Ha - CSIRO Email Leaks
Placeholder
FameLab 2017 Western Australia Semi-Final Highlights
Placeholder
Brew Ha Ha - New Hope for Premmies
Placeholder
Brew Ha Ha - Britain Goes Coal-Free
Placeholder
Brew Ha Ha - Naked Mole-Rats (SFW)
Placeholder
Brew Ha Ha - Easter Reminders
Placeholder
Meet Andrea Boyd - Space Flight Controller
Placeholder
Brew Ha Ha - Sperm Drug Smugglers
Placeholder
FameLab 2017 New South Wales Semi-Final Highlights
Placeholder
The Science of Fiction
Placeholder
Brew Ha Ha - Liquorice Poisoning
Placeholder
Brew Ha Ha - Crowdsourcing Science
Placeholder
FameLab 2017 Queensland Semi-Final Highlights
Placeholder
Brew Ha Ha - SpaceX Preps for Relaunch
Placeholder
Poly Cystic Ovary Syndrome Breakthrough
Placeholder
Brew Ha Ha - Surviving a Media Storm
Placeholder
Will This Aussie Team Win the Race to Create the Ultimate Malaria Vaccine?
Placeholder
Brew Ha Ha - New Dino Family Tree
Placeholder
How to fix things with Kyle Wiens
Placeholder
Repair or replace? iFixit co-founder Kyle Wiens
Placeholder
Special Investigation - No Alternative to Cancer