I agree with your central premise that conversions should be taught, eventually. I'm not sure I agree with your assessmen of when. I think we all want the same thing here. That is, metric should be taught first, both measuring skills and "conversion" between metric units. That instruction should be grade-appropriate beginning in early elementary grades. Any Customary or Imperial units taught should be deferred until later, I would suggest until middle school or junior high. I would teach only the most common such units (I would only teach Survey feet to surveyors, in college, for example). One guide to "common" might be those Customary units allowed for trade under FPLA. Once they learn the basics, they can learn to Google NIST SP811or Handbook 44, appendix C for more esoteric units. I would not teach Customary measurement skills, only conversion. I believe it should not be taught until kids are past arithmetric and into mathematics. The "litmus" test is not, in my opinion, whether they can multiply 8-digit numbers by hand, but whether they are capable of symbolic manipulation, in particular manipulation or cancellation of the units. They should also understand precision, either actual or implied, and where to round. That is pre-algebra and post-arithmetic. Clearly if they have to crunch numbers by hand, they would use rounded conversion factors. I'd prefer they only use exact factors, but round answers sensibly (no "decimal dust"). I have no problem deferring it until the point where calculators are allowed, and teaching them to do it correctly. In school, I would ONLY teach them to convert Customary to metric, never the reverse. The goal is to teach them to use metric, yet be able to preserve the value of data in obsolete units.
--- On Sun, 11/29/09, Pierre Abbat <[email protected]> wrote: From: Pierre Abbat <[email protected]> Subject: [USMA:46210] Re: content inch pound meter gram To: "U.S. Metric Association" <[email protected]> Date: Sunday, November 29, 2009, 9:48 AM On Saturday 28 November 2009 14:15:05 Bill Hooper wrote: > On Nov 28 , at 1:49 PM, Robert H. Bushnell wrote: > > Conversion from inch-pound units to metric > > units may be used as examples in algebra. > > There is no good reason to teach conversion from inch-lb to metric. I disagree. If all new surveys are labeled in meters, surveyors will be working with old maps and deeds labeled in feet and chains for at least another hundred years. Not everyone will need to convert, but there are enough specialties where it is needed that it should be taught. Students should not be taught conversion of pounds, until they have demonstrated that they can multiply two eight-digit numbers by hand accurately. If they can multiply two three- or four-digit numbers, they may be introduced to feet and inches. To be introduced to the survey foot, they must be able to do long division by hand with an arbitrary four-digit denominator. Conversion shall be done with the definitions of units. When converting pounds-force to newtons, for instance, the approximate factor 4.448 must not be used. One must use the exact definition of the pound and the standard acceleration of gravity. Pierre -- lo ponse be lo mruli po'o cu ga'ezga roda lo ka dinko
