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G’day from Down Under! I’m in Australia for a week’s worth of school visits starting tomorrow, and some extra time devoted exploring and research. I just saw my first kangaroo in the wild!

Aside from marsupials, the Sydney Opera House, meat pies, didgeridoos and other pleasures of Oz, I’m thinking about the metric system, or Système Internationale (SI), as it is properly known. In my presentations at schools, I refer to measurements many times. Last week while presenting at the wonderful Springfield Ball Charter School in Springfield, IL, I asked my host to make a note every time I said something like, “Light travels 186,000 miles per second” or “I’m about 6 feet tall” or “If you ate ice cream at a rate of one ounce per minute…” I wanted to know all the times I use measuring units in the American way.

Armed with his notes, I can now use conversion factors and change those archaic American measurements to sensible metric ones for my Aussie audiences. But do I want to? Does it make sense to convert a measurement to its equivalent in another system? As far as I can tell, the answer is, “Sometimes.”

I believe it makes perfect sense to say that the speed of light is 300,000 km per second and that the earth is 150,000 million kilometers from the Sun. (It’s pronounce KILO-meters, by the way — not kill-O-meters.) But should I convert when I am talking about my book on proportion, If You Hopped Like a Frog, and I say that I’m about six feet tall, and if I my tongue were as long proportionally as a chameleon’s (half as long as its body), my tongue would be three feet long? In other words, should I tell the Australian children that I am 183 cm tall, so my chameleon tongue would be about 91.5 cm? Or… to use the title example, in the States I tell my audience that a 4’6” child able to hop like a frog (meaning 20 times his or her length/height) would be able to jump 90 feet. Here in Australia, should I say that a 137 cm child able to perform a frog’s feat would thus hop 27.4 meters?

Of course not. Exact conversion often makes for complicated, daunting mathematics.

Yet I see this sort of thing in books all the time. “He walked about 25 miles (32.18 km) a day”. . . “Add two cups (473 ml) of flour” . . . “A St. Bernard can tip the scales at 200 lbs (91 kg).” If you didn’t know better, you’d think all American measurements are nice round numbers while metric measurements are ugly and unwieldy. But the fact is that whoever provided the original numbers approximated to nice, round ones. Calculate a conversion and it gets ugly. (Of course if we wrote it in the reciprocal it would be just as ugly. For instance, we could say, “A St. Bernard can tip the scales at 90 kg (198.42 lbs.)” and readers would blanche at the thought of weighing the dog in pounds!)

The best thing, I think, is not to convert, but to think metric from the start. Tomorrow, I won’t say I’m 183 cm tall. I’ll say I’m about 180 cm tall so my tongue (if I had one that was as long, proportionally, as a chameleon’s) would be 90 cm long. And so on.

The practice of converting units has kept the U.S. from switching to the metric system and joining

By Michelle Lana
Happy Halloween guys!