Ever wondered how many Fry’s you are? Or how big your house is in RAHs? Perhaps you think your appearance is up to milliHelen levels? This month Russ Swan takes a nosey around the strange world of alternative units and discovers that SI may have a few competitors…
Measuring things is at the heart of what we do in the laboratory, whether it is the size of particles in a pharmaceutical compound or the reflected spectrum of a specimen to gain clues to its composition. Whatever the job, it’s handy to have a unit to describe the measurement with. Without both a quantity and a unit to write down, it can be hard to convince the boss that we’ve actually done any work.
Most of the time, those handy units are part of a coherent measurement system that has been devised and refined over centuries and which conforms to internationally-recognised standards. Most of the time.
There are, however, some circumstances in which those units are not the right tools for the job. Because we (you and I) are intelligent science types, we can think in terms of nanometres and micrometres and not get frightened. We also know the difference between a micrometre and a micrometer. If you read the newspapers and watch the television, you will realise that the general population cannot be trusted with such complicated concepts, which is why the actual standard unit of measure for small things is the human hair.
To be accurate, the full name of the unit is the ‘times smaller than a human hair’, or TSTHH. It is a reciprocal measure, so that a high TSTHH is actually a small thing: 10 TSTHH is about the size of a human red blood cell, whereas a virus is more like 1000 TSTHH.
Reciprocal measures hold a special place in my heart. We still speak of a car with ‘high’ fuel consumption as having ‘low’ mpg, despite the fact that it has been decades since we bought fuel in gallons. At current prices, we should probably revert to buying the stuff by the teacup.
Alternative measures are everywhere. Moderately large areas are described in terms of football fields, but when discussing scientific issues of global importance – like the loss of rainforest or the size of the latest iceberg to calve itself off from Antarctica – we need something altogether more meaningful. This is where the unit known as the SoW comes into its own.
The size of Wales is a peculiarly British unit of measure which, unlike the things used to buy petrol or carrots, has steadfastly refused to be updated to the Système International. The metric equivalent of the SoW is the SoB, the size of Belgium, and for handy reference the conversion between the two is 1.5 SoW = 1 SoB. American readers might like to know that their equivalent, the SoC, is about 0.75 SoW or 0.5 SoB. Connecticut isn’t as big as you might think.
Having dealt with length and area, we must consider volume. Local councils and highway authorities have long measured the size of holes in the road using the DDB value, which helpfully describes how many double-decker buses could fit inside. Liquid volumes are of course measured in swimming pools, while larger spaces have a standard measure of RAHs, or Royal Albert Halls. Should the situation ever arise, you might be able to guess that 1 RAH is about 40 OSP (Olympic swimming pools) or 1 kDDB.
Hail the firkin
We may have been trained to use SI, and we may be familiar with the TSTHH and SoW through constant exposure, but there also exists a fully established and coherent alternative measurement structure known as the FFF system (and by established I mean that it has a Wikipedia entry). Having base units of the furlong, for length, the firkin (mass) and the fortnight (time), this provides all the measurement potential you could ever need, while simultaneously preserving the delightfully archaic units of the past. Sociologists go to great lengths to preserve dying languages and cultures, so why should these measurements be lost? And what better way to describe the top speed of a garden snail, than 78 furlongs per fortnight (fur/ftn)?
Like language, units have to evolve. Centuries ago, in the days of the ancient Greeks, a quantity that was once thought subjective was analysed and measured. Thus we know that beauty is measured in Helens, where one milliHelen is the quantity needed to launch a single ship. Today we assess popularity by a contemporary yardstick, the Fry. Laboratory News, you might like to know, has 0.5 milliFry followers on Twitter.
And sometimes, just sometimes, an unconventional unit provides a deep insight into the mysterious workings of the universe. How else can you explain the fact that, to within a fraction of a percent, one nanocentury is exactly ∏ seconds?
By Russ Swan