Metrication matters - Number 66 - 2008-11-10
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Contents
1 Feedback - notes and comments from readers 2 Editorial 3 Oddities - measurements from around the world 4 Tips - pointers and methods to make your measurements easier. 5 Signs of the times 6 Quotations 7 Q&A - readers' questions and answers 8 Rule of thumb 9 History 10 Hidden metric1 Feedback
Marion Moon wrote a few months ago to make a suggestion about my reference to the work of Méchain and Delambre in the Metrication matters newsletter number 61. Marion wrote:
Pat,
I am surprised you didn't mention Ken Adler's book on Méchain and Delambre: "The Measure of all Things: The Seven-year Odyssey and the Hidden Error that transformed the World". A very detailed history of the effort. It seemed to me that Méchain suffered from serious depression but Adler never mentioned it. I never did understand the "error" and if it truly existed. Adler is a novelist as I recall and may not have understood the changes that Méchain introduced in the measurements.
M. F. MoonYou might recall that I included part of a metric song written by Kate Gladstone in the October newsletter. Subsequently, Kate Gladstone wrote to say that her metric song is not available directly from her web site as her web page deals with handwriting and not with measurements, but she will be happy to send you a copy of the metric song if you send an email to her at In part, Kate wrote:
Dear Pat
... I don't want a horde of disappointed metric-song-seekers blaming either me or you for the song's absence from a web-site whereon it has never appeared.
2 Editorial
As you probably know NASA decided to use SI metric units for engineering and operations after the debacle with the Mars Climate Orbiter. But NASA seems not to have succeeded in changing its non-metric culture. They have decided to issue all measurements to the public in both metric units and also in old pre-metric measures, so it would appear that their resolve to 'Go metric' after the Mars Climate Orbiter disaster is already starting to break down. Look at passages like this from the web site at http://phoenix.lpl.arizona.edu/index.php :
The image shows four round pits, only 5 microns in depth, that were micromachined into the silicon substrate, which is the background plane shown in red. This image has been processed to reflect the levelness of the substrate.
A Martian particle – only one micrometer, or one millionth of a meter, across – is held in the upper left pit.
As you can see, the length of a single micrometre is written in three ways in just two paragraphs, and the mile is alive and well at http://phoenix.lpl.arizona.edu/05_22_pr.php where miles are mentioned 5 times but there is no mention at all of kilometres.
3 Oddities
You've heard of nano technology that is done to nanograms at distances of nanometres in nanoseconds. The next frontier will be atto technology where things are done in attoseconds (10^-18 s). See http://www.bath.ac.uk/news/2007/11/16/light-article.html for details.
4 Tips – pointers and methods to make your measurements easier.
If you are converting from old pre-metric measures to metric units, be careful with what is originally only a rough approximate measurement and then try to reflect that in your result.
For example, in the USA it seems to be commonly assumed that a male of average height and weight is 180 lb. Although this converts to 81.647 kg on a calculator, you need to do a little more with this result. Think about the initial accuracy of the estimate of 180 lb. It's unlikely to be accurate to the nearest lb or even 2 lb, so it's quite reasonable to round off the original 180 lb to 80 kilograms. You will always be within 2.5 kilograms if your estimates end in 0 or 5.
Generally, metric conversion is not a good idea, so if you can avoid conversions do so. See /docs/MetricConversion.pdf for some of the pitfalls.
5 Signs of the times
Some time ago, Nat Hager III from Pennsylvania, reported to the USMA list on a visit to a hardware store. Nat wrote:
Saw a couple pleasant surprises at the Lowe’s hardware store this morning:
- 8 mm and 18 mm plywood paneling in the lumber department, Lefarge spackling compound in 2.5 L tubs (SI-only) in the drywall section, and household surge protectors rated in Joules. Guess it was easier to use SI than make up some convoluted units, such as horsepower-minutes.
Nat
You can join the United States Metric Association (USMA) mail list at http://lamar.colostate.edu/~hillger/listserv.htm
6 Quotation
Though no one can go back and make a brand new start, anyone can start from now and make a brand new ending. – Author Unknown
7 Q&A
Question:
Why is the speed of light used to be the standard for the length of a metre?
Answer:
The reason for this is that the speed of light is always the same speed everywhere in the Universe. Anyone with the right equipment can verify the length of a metre and it will be the same wherever this is done. The metre is based on the speed of light (at exactly 299,792,458 metres per second). Since 1983 October 21, one metre has been defined as the distance light travels in a vacuum in 1/299 792 458 of a second.
Martin Hogan wrote:
Hi Pat,
I have been asked to give a presentation in Coffs Harbour next week about Energy & Global warming. I would like to quote and acknowledge your article " A word about Global Warming". Simplifying the language is one of my passions especially units of measurement. Unless I hear to the contrary I will assume that it is OK to quote & acknowledge you. Thank you for your efforts
Regards
Martin Hogan
And I replied:
Dear Martin,
Go for it. The more people who understand that obfuscation is holding back real information about climate change (and peak oil) the better for all of us.
Cheers,
Pat Naughtin
You can find the article that Martin refers to at: /docs/AWordAboutGlobalWarming.pdf
8 Rule of thumb
When you are considering which fuel you will choose for a new car, these approximate figures for the energy content of fuels, in megajoules per litre, might be useful to consider if you plan to reduce your energy footprint:
- Diesel contains 39 MJ per litre,
- Gasoline 35 MJ per litre,
- Bio-Diesel 31 MJ per litre, and
- LPG contains only 22 MJ per litre.
9 History
The performances of ancient Roman charioteers were carefully recorded. They made lists of the wins by various charioteers and also counted the number of times that they came second. But none of the Roman sports administrators ever calculated the winning percentages. I suppose it might have had something to do with working out how to divide DVII by CCCXIII and then multiplying by C to get the percentage.
10 Hidden metric
The Red Cross web site in the USA says:
You must weigh at least 110 Lbs to be eligible for blood donation for your own safety.This looks a lot like 50 kilograms to me.
Cheers,
Pat Naughtin
Geelong Australia
Pat Naughtin is a writer, speaker, editor, and publisher. Pat has written several books and has edited and published many others. For example, Pat has written a chapter of a chemical engineering Encyclopedia, and recently he edited the measurement section for the Australian Government 'Style manual: for writers, editors and printers'. Pat has been recognised by the United States Metric Association as a Lifetime Certified Advanced Metrication Specialist.
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