J. Ward wrote: 'As a physicist I would speak in terms of "per meter squared."' Maybe so (and we had a discussion on this list a few years ago, involving that same ultimate reduction), but it is something that neither the physicist nor the layperson can readily visualize (although the physicist can rationalize its use). Your comments on average fleet mileage serve to remind us of the need to do a better job of teaching mathematics. It's the classic case of failure to recognize that, because the calculation has to be done on the basis of consumption, rather than range, one must average the reciprocals and then use the reciprocal of the result. For the car manufacturers to arrive at an advertised average in any other way should be considered fraud--and prosecuted as such. And, obviously, Congress should not be so easily fooled by the antics of a self-serving industry (and should write the formula to be used into the law). In the meantime, distance traveled per unit volume (km/L or mpg) tends, I believe, to be more meaningful to the person doing the traveling and buying the gas. For that reason, it makes metrication more acceptable to the average person. Bill Potts, CMS Roseville, CA <http://metric1.org/> http://metric1.org [SI Navigator]
_____ From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of J. Ward Sent: Sunday, January 27, 2008 20:22 To: U.S. Metric Association Cc: U.S. Metric Association Subject: [USMA:40254] Re: convenient numerical values The biggest disadvantage of km/L is to give a huge loop-hole to auto maker who sell gas guzzlers. For example, the U.S. government has requirements for fleet averages in terms of miles/gallon. Imagine I'm an automaker and I want to sell muscle cars or monster trucks that average 5 miles/gallon. If I can sell a single 55 mpg economy car for every 5 mpg gas-hog I sell to get a respectable fleet average of 30 mpg. This misleads the public (and most Congressmen!) into assuming that the cars sold use the same amount of fuel to go a given distance as two vehicles that individually average 30 mpg. Nothing could be further from the truth! In fact, the two vehicles use the same amount of fuel to go a given distance as two vehicles that individually average 9 mpg. Now work the same problem in L/100 km. The economy car uses 4.3 L/100 km. The guzzler uses 47 km/100 L. The fleet average is 26 L/100 km, which accurately reflects the huge amount of fuel used by the fleet per kilometer driven. Clearly, Europe is doing a lot better than we are in terms of how they measure fuel consumption. Finally, I would add that an SI purist would never use km/L. As a physicist I would speak in terms of "per meter squared." Therefore, I prefer L/100 km over km/L, clumsy as it may seem at first glance. J. Bill Potts wrote: Clearly, km/L is the more rational. Bill Potts Roseville, CA http://metric1.org [SI Navigator] -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Ziser, Jesse Sent: Sunday, January 27, 2008 17:38 To: U.S. Metric Association Subject: [USMA:40252] Re: convenient numerical values --- Pat Naughtin <mailto:[EMAIL PROTECTED]> <[EMAIL PROTECTED]> wrote: On 2008/01/28, at 8:10 AM, <mailto:[EMAIL PROTECTED]> <[EMAIL PROTECTED]> <mailto:[EMAIL PROTECTED]> <[EMAIL PROTECTED]> wrote: Deciliter in the denominator is conventional medical practice in which "convenient numerical values" are considered more valuable than coherence of units. The same is true for grams and mg in medical practice. Gene. Dear Gene and All, The expression you use here, 'convenient numerical values' appears quite often in many different contexts and, it seems to me, that this is at the expense of an efficient metrication upgrade. Another example is the change from millibars to hectopascals in meteorology where the numbers stay the same while the unit name changes without gaining the benefits of the coherence of the metric system or the convenience of the 'rule of thousands'. I am sure that there are many other examples. I'd like to offer another possible example of violation of the rule of thousands. I keep seeing L/100 km in fuel efficiency contexts. I also occasionally see km/L but it appears to be rarer. km/L is clearly more "thousandy", and also has the debatable advantage of being "distance per volume" just like MPG. Besides, "L/100 km" seems an awkward mouthful. Is this really the preferred unit? I'm thinking about getting metric mileage bumper stickers for my friends and family (most of whom I'm sure would enthusiastically accept and display them) and I was wondering if anyone had any other opinions on the km/L versus L/100 km issue. I've been unable to find much about it online. Thanks. ____________________________________________________________________________ ________ Be a better friend, newshound, and know-it-all with Yahoo! Mobile. Try it now. http://mobile.yahoo.com/;_ylt=Ahu06i62sR8HDtDypao8Wcj9tAcJ
