[SCMP Column] Absolute measurement

February 18, 2017


After 138 years of rule from inside a triple-locked vault in Sevres outside Paris, Le Grand K seems about to be retired. The arcane world of metrology is afire. I for one will be sad. At the very least it is the end of measurement as we know it. At worst it feels like measurement gone mad.

For those unfamiliar with the fastidious world of metrology, Le Grand K is a little lump of platinum-iridium alloy that was forged in 1879 to provide the world with the definitive measure of a kilogram. Since it was forged – and benchmarked against six official copies – Le Grand K has been allowed out of its vault only four times, for a quick but careful clean, and to be compared against its six copies.

And here is the crisis: when last allowed out in 1991, it was found to be 50 micrograms lighter than the average of its copies. That, by the way, is about the weight of a fly’s wing. Le Grand K’s guardians are not sure if it is Le Grand K that has slimmed, or whether its comparators have gained weight. But for the world of measurers, this was not good news, and something had to be done about it.

The solution, now almost ready to be unleashed on the world of measurement, is to anchor the future kilogram to Planck’s constant, a fixed quantity linked to E=MC2 and quantum theory that specifies the amount of energy carried by a single particle of light, or photon.

Obvious, right? Call me an old fogey, but forgive me for feeling that this is measurement gone mad. To base the cost of my kilo of carrots on some exotic constant rooted in quantum theory seems nothing like as comfortable as anchoring it to a lump of metal – even a lump that has been in hiding for most of its 138 year life.

It seems in all areas of measurement, our measurers’ love affair with quantum constants and an endless quest for infinite accuracy has led them far from the messy, sweaty world in which most of us measure our surroundings. Take time, and how we measure a second. In the good old days, a second was 1/86,400th of the time it takes for earth to rotate relative to the sun. Since 1967, it has been defined as how long it takes for 9,192,631,770 cycles of radiation in a cesium 133 atom – or something like that.

Or take the meter, which in 1791 was defined by the French Academy of Sciences as one ten-millionth of one fourth of the world’s circumference. The vault that houses Le Grand K quaintly also houses the original benchmark meter-length rod created at the time. But since 1983, a meter is the distance light travels in a vacuum in 1/299,792,458th of a second. Again, obvious, right?

There are perhaps some instances where such extreme efforts at accuracy are justified. When NASA’s Mars Climate Orbiter was lost as it entered Mars’ atmosphere on September 23 1999, obviously the very tiniest margins of error might have been responsible for the catastrophe. But no. It turned out that NASA was using metric measures to calculate how much thrust was needed to put it into the right orbit, while Lockheed Martin, who provided them with relevant software was using pounds. As the inquiry reported, the ground-based computer software “produced output in units of pound-force-seconds instead of newton-seconds specified in the (NASA) contract.” Whoops.

I feel sort of sentimental about those innocent early days when an inch was the width of a man’s thumb, which was 1/12th of a man’s foot (reduced by 20% when Britons converted from large Anglo-Saxon feet to daintier Roman feet). A yard was what King Henry I decided was the distance from his nose to the thumb of his outstretched arm. And an acre was the area of land an ox-drawn plough could cover in a day.

As I order a pint of beer, or buy a catty of prawns in the wet market, it is such sweaty concepts that guide me on whether I am being cheated or not. These exotic quantum constant measures seem more than anything to be make-work concepts for unemployed measurers.

Don’t get me wrong. I passionately agree that accurate measurement is critical – and is becoming even more fastidious as we move to nano-technologies and atom-level devices. It is important to have science that can prove definitively that Volkswagen has been ever-so-carefully rigging the results of its diesel engine emissions tests. Or that food processors have or don’t have gluten in a product. Or can explain why the artificial island being built in the Pearl River as part of the Hong Kong-Zhuhai bridge has drifted by up to six meters.

But for most of us, for most of the time, accuracy beyond a certain very average level is not just incomprehensible. It is irrelevant and sometimes misleading. As the British Government says in its National Measurement System, we need accuracy “within legally controlled tolerances”.

At the end of May last year, Britain’s GDP in US$ terms was $661bn. At the end of the year, after the Brexit vote and a 12% devaluation of sterling, it was down about US$73bn. In sterling terms it was pretty much unchanged. What do we measure? There is not a metrologist in the universe who can answer that.

If you open a barrel of whisky after it has been ageing for 20 years, you will always find some whisky has been lost – no matter how meticulously you fill it to the brim before it is sealed. Distillers call it “the angel’s share”. I don’t think there are many angels that are metrologists.

So as Le Grand K goes into genteel retirement after 138 years of service, I think we should mourn a little, and ask whether we perhaps should cherish, alongside these newfangled quantum constant measures, a set of down-to-earth measures that help us manage our normal lives. As Britain’s measurers argue: “Measurement provides structure, removes chaos, reduces waste, ensures open and fair markets, supports precision where required, and saves lives, money and time.” Planck’s constant somehow does not give me that.
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