You are correct on the preferred practice. However, if you apply it to a 10 L/100 km fuel economy, you wind up with 100 µL/m (or even 10^-7 m² if you further "simplify"). I believe that would be inconvenient for the average person to use for the calculation most relevant to him. Similarly, I believe your figures would be better expressed as megajoules per kilometer (certain very small and very large vehicles may require a different prefix in the numerator).
--- On Fri, 9/18/09, Pat Naughtin <[email protected]> wrote: From: Pat Naughtin <[email protected]> Subject: [USMA:45831] Re: Fuel efficiency – joules per metre To: "U.S. Metric Association" <[email protected]> Date: Friday, September 18, 2009, 6:57 PM 2 I think that it is preferred practice in SI to have the denominator in a unit without a prefix and to apply any prefix to the numerator. In this case, kilojoule per metre (kJ/m) would be preferred to joules per kilometre (J/km). However, that said, I believe that the simplest SI unit applied with whole numbers is the best possible solution. Cheers, Pat Naughtin Author of the ebook, Metrication Leaders Guide, that you can obtain from http://metricationmatters.com/MetricationLeadersGuideInfo.html PO Box 305 Belmont 3216, Geelong, Australia Phone: 61 3 5241 2008 Metric system consultant, writer, and speaker, Pat Naughtin, has helped thousands of people and hundreds of companies upgrade to the modern metric system smoothly, quickly, and so economically that they now save thousands each year when buying, processing, or selling for their businesses. Pat provides services and resources for many different trades, crafts, and professions for commercial, industrial and government metrication leaders in Asia, Europe, and in the USA. Pat's clients include the Australian Government, Google, NASA, NIST, and the metric associations of Canada, the UK, and the USA. See http://www.metricationmatters.com for more metrication information, contact Pat at [email protected] or to get the free 'Metrication matters' newsletter go to: http://www.metricationmatters.com/newsletter to subscribe.
