Why SI Is Cool

The Système International d’unités (or SI, or the “Metric” system) is still less than popular in the U.S. My guess is that this is due to a lack of familiarity, or just basic intellectual inertia: people are most comfortable with what they already know.

If you do much serious scientific or engineering work, though, the problem of unit conversion comes up constantly (pardon the pun). Working in electronics, unit conversion is needed to determine how long a particular capacitor will power a microcontroller at a given current draw, or what value of resistor is needed in order to limit current through an LED to an acceptable value.

This is where SI units really start to become useful. For example, take the following statement of equivalencies, found in the Wikipedia article on the farad (the SI unit of capacitance):

SI Equivalents of one Farad (unit of capacitance)

SI Equivalents of one Farad (unit of capacitance) Source: Wikipedia

At first, all this doesn’t look very simple. But look closer. There are no conversion constants! No “12 inches to the foot,” no “5,280 feet to a mile,” no “divide by this weird, irrational magic number to make the units fit.”  Numerically (without the units), the whole statement above just says 1 = 1 = 1 = 1 = 1 = 1 = 1 = 1 = 1 = 1. Everything just works!

It took a lot of work to come up with a set of units that all work together like this (a cube ten centimeters on a side has a volume of one liter; fill it with water and it has a mass of one kilogram; accelerating it at one meter per second per second requires a force of one Newton etc). All of the conversions are either one-to-one, or based on some power of ten. There are a few arbitrary choices (water tying the kilogram to the meter etc), but the whole system is very numerically consistent.

Pop quiz: How many inches in a mile? You’d need a calculator, or at least a pencil and paper to find out that it’s 63,360 — and that’s if you remember the conversions.

Now try it in metric: How many centimeters in a kilometer? Easy: 1000 meters in a kilometer, and 100 centimeters to the meter. The answer is 100,000.

It’s not a Big Liberal Plot — it just makes doing science and engineering a lot easier.

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3 Responses to Why SI Is Cool

  1. Hear hear! As you say, so many things are very much easier in metric. I think we’re a bit further down the road here in the UK, but a lot of people over the age of about 60 will say things like “I don’t understand all this metric stuff – it’s too complicated”.

    Although a bit before my time, people said similar things about the change from pounds, shillings and pence to “new pence”. Splitting the restaurant bill must have been much harder then since it involves a different number base for each unit. Bah!

  2. Helen says:

    The best example of the difference between metric and US measures is calculating irrigation. In metric, the calculation is a simple arithmetic function. In US measures, it is several lines of conversion factors.

  3. Daniel says:

    It is common among those Americans that feel the US should metricate, to try to sell the metric system on simplicity. There is nothing more simpler then what you already know or pretend to know, and no matter how logically organized SI is, the majority of Americans will always find it confusing.

    The only way to convince people metrication is necessary is to link it to economic prosperity. Metric countries are becoming prosperous quickly and the US is in decline. Companies needing or wanting to metricate will do so by opening a factory in a metric country then risk the added costs of not only training but the resistance that will ensue.

    Consider this:

    The ACME widget factory is being pressured by its potential international customers to metricate its products before they will buy. ACME decides to investigate and discovers that it can’t economically produce a metric product in inches. The mistakes and tolerance issues will add cost and make the product uncompetitive.

    So they go to the employees and tell them the situation. Instead of the employees recognizing the importance of this, they think of their own personal comfort and begin to scream. AAAAAAHHHHHH. No, we will never use metric. We are Americans we don’t do metric. Make the world use our standards. Why must we who are the best in the world lower ourselves to their level? Never! Never! Never!.

    So the company has no choice but to close it doors and relocate to a metric country to have its products made. The American plant closes and all the American workers become unemployed. Other companies are doing the same thing and unemployment increases and along with it poverty.

    A far fetched scenario? Nope! It is already happening. Companies are leaving to get away from workers who won’t conform.

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