Measurement is perhaps the most important defining characteristic of Lean Six Sigma and what its practitioners, popularly known as Black Belts, do. So what better gift for the Black Belt on your holiday gift list than a book on the history of measurement titled “World in the Balance: The Historic Quest for a Universal System of Measurement” by Robert Crease and published by W.W. Norton.
A good unit of measurement, writes Crease, must satisfy three conditions. It has to be easy to relate to, match the things it is meant to measure in scale (no point using inches to describe geographical distances) and be stable. Crease, who teaches philosophy at Stony Brook University on Long Island and writes a column for the magazine Physics World, describes man’s quest for that metrological holy grail. In the process, he shows that the story of metrology, not obvious material for a page-turner, can in the right hands make for a riveting read.
The earliest known units met the first two of Crease’s requirements well. Most were drawn from things to hand: the human body (the foot or the mile, which derives from the Latin milia passuum, or 1,000 paces) and tools (barrels, cups). Others were more abstract. The journal (from jour, French for “day”), used in medieval France, was equivalent to the area a man could plough in a day with a single ox, as was the acre in Britain or the morgen in north Germany and Holland.
But no two feet, barrels or workdays are quite the same. What was needed was “a foot, not yours or mine”. Calls for a firm standard that was not subject to fluctuations or the whim of feudal lords, grew louder in the late 17th century. They were a consequence of the beginnings of international trade and modern science. Both required greater precision to advance.
In response the metre, from the Greek metron, meaning “measure”, was ushered in, helped along by French revolutionaries, eager to replace the Bourbon toise (just under two metres) with an all-new, universal unit. The metre was to be defined as a fraction of the Paris meridian whose precise measurement (in toises) was under way. Together with the kilogram, initially the mass of a decaliter of distilled water, it formed the basis of the metric system.
Successful French metrological diplomacy meant that in the ensuing decades the metric system supplanted a hotchpotch of regional units in all bar a handful of nations. Even Britain, long wedded to its imperial measures, caved in. (Americans are taking longer to persuade.) In 1875 Nature, a British magazine, hailed the metric system as “one of the greatest triumphs of modern civilisation”. Paradoxically, Crease argues, it thrived in part as a consequence of British imperialism, which all but wiped out innumerable indigenous measurement systems, creating a vacuum that the new framework was able to fill.
For all its diplomatic success, though, the metre failed to live up to its original promise. Tying it to the meridian, or any other natural benchmark, proved intractable. As a result, the unit continued to be defined in explicit reference to a unique platinum-iridium ingot until 1960. Only then was it recast in less fleeting terms: as a multiple of the wavelength of a particular type of light. Finally, in 1983, it was tied to a fundamental physical constant, the speed of light, becoming the distance light travels in 1/299,792,458 of a second. (The second had by then itself got a metrological makeover: no longer a 60th of a 60th of a 24th of the period of the Earth’s rotation, it is currently the duration of 9,192,631,770 periods of a phenomenon called microwave transition in an atom of caesium-133.)
Now the kilogram, the last artefact-based unit, awaits its turn. Adding urgency is the fact the “real” kilogram, stored in a safe in the International Bureau of Weights and Measures in Sèvres, near Paris, seems to be shedding weight relative to its official copies. Metrologists are busy trying to recast it in terms of Planck’s constant, a formula which is deemed cosmicly inviolate, as is the speed of light (pending further findings from CERN, anyway).