Pat, I totally agree. Sorry if I gave the wrong impression. I too feel quite strongly that the only way to learn and use metric properly is to get to know the world around you in metric units and forget about the others. I too have some mental guages for that purpose, e.g the width my hand is about a decimetre, the height of an internal door is 2 m etc.
However the purpose of the easy conversions is as an aid to coping with being bombarded with non-metric data from sources outside of your control, for example in the media. Not very long ago there was a big European news item about that new airbus jet. In the UK media there was a mixture of reporting (length, wing span etc), some in metric some in imperial. If it was featured in the American news I'll bet it was all in feet. When I encounter such things I start doing mental conversions. The main thing to remember is that the primary reference for a metric thinker is the metric system, just as imperial is for many (possibly most) people in the UK. But whilst the ludicrous (and totally unnecessary) situation of multiple measures exist there will always be a need for conversion. Regards Phil > -----Original Message----- > From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] > Behalf Of Pat Naughtin > Sent: 04 March 2005 00:40 > To: U.S. Metric Association > Subject: [USMA:32350] Re: Conversion > > > Dear Phillip, > > With respect, I don't think that moving from a mindset based on the > inch-ounce family of old measures to a mindset based on conversion factors > between old and metric units is the way to go. > > I believe that the best way to achieve metrication is by the direct route > where you develop a new metric mindset without referring to conversion > factors at all. > > I have interspersed some ideas below based on your original examples. > > on 2005-03-03 23.49, Philip S Hall at [EMAIL PROTECTED] wrote: > > > We all (or most of us here) like to think metric but are having > to put up > > with those wretched non-metric units that plague us in everyday > life. Well > > I've a few methods that in some cases can make it a little > easier to convert > > mentally. > > > > 1 in = 2.5 cm (exact conversion 1 in = 2.54 cm) > > Multiply by 10 and divide by 4, or halve and halve again, example: > > 18 in (x 10) --> 180 (halve it) --> 90 (halve it again) --> 45 cm > > > > Measure the width of the nail on your little finger. It is about > 10�millimetres wide. > Measure the widths of your other three fingers. They are all about > 20�millimetres wide. > Look at the width of your fist across the knuckles. It is about > 100�millimetres wide. > Remember these and you can estimate small lengths and distances quite > readily using your 'handy' references. > > > 1 ft = 0.3 m (exact conversion 1 ft = 0.3048 m) > > multiply by 3 and divide by 10, example > > > > 50 ft (x 3) --> 150 (div by 10) --> 15 m > > > > 1 yd = 0.9 m (exact conversion 1 yd = 0.9144 m) > > Reduce by 10 %, example > > > > 200 yd (subtract 10% of 200) --> 180 m > > Mark out a length of ten metres between your house and your garage, or > between the car park and your office at work. Practice walking > this in a set > number of steps until you can readily and reasonably accurately 'step out' > 10�metres. By slightly stretching my paces I can step out ten > metres in ten > steps. > > > 1 mile = 1.6 km (exact conversion 1 mile = 1.609 344 km) > > Multiply by 3, halve it and add 10% of the original, example > > Most people walk at about 100�metres per minute. If you walk reasonably > briskly for ten minutes, you will have walked 1�kilometre. If you walk for > 20 minutes you will have walked 2 kilometres. > > > 500 mile (x 3) --> 1500 (halve it) --> 750 (add 10% of 500) --> 800 km > > Picture a map of the continental USA. At its widest it is 4400 kilometres > and its maximum length is 2600 kilometres. Estimate long distances as > fractions of this map. > > As a side issue, the continental USA averages about 4 megametres wide by 2 > megametres North to South, so it has an area of about 8 square megametres > (7.827�620�square megametres to be precise). > > As another side issue, the continental USA is approximately the > same size as > Australia, which is also about 4�Mm by 2�Mm or about 8�square megametres > (7.686�849�square megametres to be precise). > > > 1 lb = 0.45 kg (exact conversion 1 lb = 0.453 592 37 kg) > > Halve it and reduce by 10%, example > > 180 lb (halve it) --> 90 (subtract 10%) --> 81 kg > > Hold a litre bottle of Coke or Pepsi until you know the feel of a > kilogram. > Do the same with two litres to feel 2 kilograms. My mother in law > once won a > 'guess the mass of the baby' competition because she remembered > the feel of > a 4 kilogram bag of flour as she guessed that the baby was a little less > than this at 3.8 kilograms. > > Remember that the average North American male has a mass of about > 85�kilograms and the average mass of a female is about 75 kilograms. When > you walk into a room full of people scan the room to find the average male > and the average female; knowing that they are close to 85�kilograms and > 75�kilograms respectively you can then guess at the mass of the others. > > Heights can work the same way. Knowing that the average height of a North > American male is about 1.7�metres and a female is 1.6�metres you > can quickly > find the average height people at a party and then estimate > everyone else's > height by knowing that the width of your fist is 100�millimetres or 0.1 > metres. By the way, it is quite difficult to estimate people's height to > much greater precision than about 50�millimetres; so if you are having a > height guessing competition its best to keep your answers to one decimal > place. > > > Please note one thing though. If you are converting from what > is originally > > only a rough approximate measurement try to reflect that in the > result. For > > example, in the US it seems to be commonly assumed that someone > of average > > height and weight is 180 lb. The above example shows this > converts to 81 kg, > > but since the estimate is unlikely to be accurate to the > nearest lb or even > > 2 lb, it would be better to regard the equivalent as 80 kg (nearest 5 kg > > say). > > I heartily agree with you on this. Too many people build in false > levels of > precision when they do conversions. If you avoid doing conversions as I > suggest above, you will also sidestep this problem. > > Cheers, > > Pat Naughtin ASM (NSAA), LCAMS (USMA)* > PO Box 305, Belmont, Geelong, Australia > Phone 61 3 5241 2008 > > Pat Naughtin is the editor of the free online monthly newsletter, > 'Metrication matters'. You can subscribe by going to > http://www.metricationmatters.com and clicking on 'Newsletter'. > > * Pat is the editor of the 'Numbers and measurement' chapter of the > Australian Government Publishing Service 'Style manual � for writers, > editors and printers', he is an Accredited Speaking Member (ASM) with the > National Speakers Association of Australia, and a Lifetime Certified > Advanced Metrication Specialist (LCAMS) with the United States Metric > Association. > > This email and its attachments are for the sole use of the > addressee and may > contain information that is confidential and/or legally privileged. 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