Visiting Canada last April and again in August, I found the Fibonacci series (1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, . . .) useful in converting between metric speed limits and my non-metric speedometer. Each Fibonacci number is the sum of the previous two, and the ratio of each adjacent pair successively approaches the Golden Section (roughly .618). The Golden Section is fortuitously very close to the ratio of kilometer to mile (roughly .621). That means that 2/3, 3/5, 5/8 -- and 21/34 or 55/89, if you are an idiot savant -- are successively closer rule of thumb approximations for kilometer/mile conversion. In other words, if the speed limit is 60 kilometers per hour, that comes out to something like 40, 36, or (best of all) 37.5 American miles per hour, any of which is precise enough to allow you to calculate an appropriate speed in miles per hour.
Anyway, on the long dull trip from Detroit to Toronto, I was ethnocentric (patriocentric?) enough that I couldn't help thinking of kilometers as 'Canadian miles' -- like Canadian dollars, they look like miles but it takes a lot more of them to cover the same drive, or purchase, as the case may be. As of today, the ratios have finally converged, and Canada's dollar, at less than U.S. $0.62, is worth as little as its mile. As long as it doesn't drop much further, this will simplify calculations for the millions of Americans who visit each year in search of bargains.
1. For huge amounts of useful information on Golden Section and the Fibonacci numbers, see the Fibonacci Numbers and the Golden Section page at the University of Surrey. Online Conversion will provide hours of nerdy fun to those who can't help wondering how many cubits are in a furlong or how many pecks in a hogshead.
2. Canadians worry way too much about supposed U.S. plans to annex various provinces. From what I've seen of Canada (a huge swatch of Ontario), they can relax. We've already got Ohio with its strip malls and soft-rock radio stations: what do we need Canada for?