I agree with his main thrust, that in order for something to be useful, it must be used. i.e., to really grok a measurement, like the meter or centimeter, you need a visceral understanding of its magnitude. I can pick up a object and guess its weight in pounds within 10% as long as it’s not too heavy. I can’t do that in kilograms without first doing the pounds and then converting in my head. Same with meters, although I’m better there, and despite my work, I’m absolutely crap with kilometers per hour.
It’s all about familiarity. During college, I worked with metric (SI) units the majority of the time while taking engineering classes. I heartily detested any moment where I was forced back upon english (imperial)1, but as Jim mentions, we didn’t do any familiarization with the metric units beyond our calculations. It wasn’t until I entered the workplace and started boring holes in things, or now building roads, than I started applying numbers to real world objects2.
So, I know exactly what it’s like to have a four 12′ lanes with a 32′ median, perhaps a 10′ shoulder. In metric, that’s…ummm…3.6 meter lanes with a 10 meter median and 3 meter shoulders? I just don’t think in meters, and I’m trained! What do we expect of the rank and file grocery shopper who only cares about how much that gallon of milk costs, not the fact that instead of $3.99 per gal, it’s $1.05 per liter. What the hell is is a liter anyway?
In an interesting bit of history, the U.S. Federal Highway Administration tried to do a conversion from imperial to metric back in the 90′s. The intention was to have a 5 year switchover and then all federally funded projects would be required to be metric. This crashed and burned due to politics. Amusingly (if you have a macabre sense of humor), this has made it more difficult in the long run to pursue metrification in the highway industry because so many people have bad tastes in their mouths about the on again off again metric switch. A lot of highway projects were caught in the middle, had to be converted from imperial to metric, then ended up being converted from metric back to imperial3. Many decision-making highway engineers and officials were in charge of projects that got mangled in this fashion and have a severe distaste for any FHWA-mandated switchover.
The upshot is, the U.S. remains the only first-world country to not have officially adopted the metric system. We maintain this high-horse with the company of two other leading countries, Myanmar and Liberia.
Should we convert? Yes. Will we convert? Not in the next ten years.
1: yes I know there’s a difference between Imperial and U.S. Customary Units. I’d rather type “imperial” though.
2: let’s not forget the time I spent working in feet, inches, and sixteenths while doing wood projects at home.
3: this is a difficult process, not nearly as easy as you might think.