This euros/km equation is easy to grasp

UPDATED: 9/15/11 9:22 am ET

It's a rare snappy slogan that works well both in miles and metric, in dollars and euros.

The Opel Rak e, a diminutive two-seater electric vehicle with the seats in tandem formation, is just that.

GM Europe boss Nick Reilly declared at the Frankfurt auto show that this was a "one euro" car. He meant that's what it would cost to drive the car 100 kilometers.

It was my job, editing the article about the car, to translate those numbers into ones Americans could understand. What I got, based on today's exchange rate, was a car that costs 2 pennies a mile.

I can understand that. It's a marketing slogan that writes itself.

EDITOR'S NOTE: The conversion to U.S. mileage has been corrected from just over a penny a mile to 2 pennies a mile.