A few weeks ago I wrote about the bicentennial of the metric system. This week I want to return to the topic of measurement because I had such an overwhelming response to that column.

Our ability to measure sets us apart from, say, llamas and horned toads, because measurement is the process of counting how much of a sensory signal exists, and so far as we know, no other animals can count.

Simply counting things in itself wouldn’t count for much if we couldn’t communicate, though. Through language, we’re able to tell others what we have measured, which enables us to describe things we’ve seen, contract with others for trade or exchange, and control various processes.

Just think about all the things you rely on measurement for. You get up and put on clothes which were measured to fit your body; you take your breakfast from a refrigerator whose temperature is measured and controlled by a thermostat; you listen to a radio tuned to a station identified by the measurement of its broadcast wavelength; you drive to work in a car built from standardized parts; you are careful not to exceed the speed limit, measured in kilometres per hour, and rely on the measuring device called a speedometer to do so; and on, and on, and on.

To a large extent our technological world is the product of our measuring ability. But of course measurement is a lot older than modern technological civilization.

Time was one of the earliest things to be measured because the passage of time can easily be marked by counting existing units–days, lunar months, seasons, years. Space can also be easily measured using our own bodies, which is why the earliest units were things like spans (thumb to little finger on a spread hand), cubits (elbow to finger tip), and, of course, the foot. Once you have a unit of length, you can measure four fundamental qualities of space: distances, areas, volumes and angles. Early civilizations did just that, even though those human-based units of length aren’t exactly what you’d call standardized. (Consider a jockey. Now consider Magic Johnson.)

Finally, our own senses also enable us to easily measure force. We can count, for example, how many stones of a particular size one person can carry, and thus judge how much force that person is capable of exerting.

But our own senses could only take us so far. It wasn’t long before we began creating tools that were more accurate and more sensitive.

Every measuring instrument has three main components: a sensor, which detects the phenomenon to be measured, a counting mechanism, and a display, which enables us to know what the count is, or at least when a certain count is reached. Sometimes there is also a transducer, which converts the phenomenon into some other phenomenon which is more easily measured. Thus, in a speedometer, a flexible cable rotates at the same speed as the wheel, and a magnet connected to the cable creates a field that varies according to how fast the cable is spinning. That field then deflects the speedometer needle.

Converting the response of the instrument to some kind of agreed upon units (i.e., kilometres per hour) is called calibration. How well that conversion is carried out is called accuracy.

For most of mankind’s existence, lack of accuracy hasn’t been a problem. The ancients didn’t worry about being off a half-hour here or a centimetre there. Even in the steam engines that powered the Industrial Revolution accuracy was of little concern; as long as adjacent parts were compatible, who cared if the same parts in other engines were a completely different size? But those mutually incompatible engines made mass production possible, and mass production means interchangeable parts, which do require accurate measurement.

So does science, among other things to ensure that results obtained by one scientist can be repeated by another. Greater and greater sensitivity of measurement was needed, as well, as the material world was examined in finer and finer detail.

The metric system, as I mentioned, was born because of the need for common units of measurement. As a reader recently pointed out, it has an additional benefit in that many of its units can be defined in terms of each other (i.e., a kilogram is equivalent to the weight of one liter of water; a joule is the energy equivalent to the work performed as the point of application of a force of one newton moves through one metre, and so on), which helps relate many physical phenomena to each other, a basic goal of science.

We’ve now reached the point where we can measure things with mind-boggling accuracy. You probably know that this is a leap year, with an extra day added; you might not know that 1990 was also a leap year, except instead of having a whole day added, it was only extended by one second. That “leap second” was necessary because the length of the day can vary by a thousandth of a second over a period of as little as two weeks, creating an ongoing “error” that adds up. This means a second can no longer be defined as 1/86,400 of a day–the rotation of the Earth isn’t accurate enough. Instead a second is defined as 9,192,631,770 waves emitted by a cesium atom when a certain change is artificially induced in their internal state.

Measurements this accurate depend on technology that has only been available for the last three or four decades. Reader L. A. Riederer of Regina, a senior citizen with a background in the sciences, noted that during the Second World War their tools could only measure tolerances to within three decimal places–but that was all right, because their slide rules were also accurate only to three decimal places.

He wrote, “I recall during World War II when we had (what we thought) a computer-like breakthrough in calculating the height of aircraft over distant anti-aircraft gun installations–at the heart of our equipment was an appropriately shaped hardwood cam to translate the cosine function. What a contrast to today’s computer capabilities!”

Indeed. But it worked–and it’s proof of the ingenuity people have always applied in response to the human need to measure the world around us.

And if you’re wondering how I measured the “overwhelming” response to the earlier column on metric–well, I had two comments on it.

By my column-writer’s standard of measurement, that’s overwhelming.

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