Metrication matters  Number 93  20110210
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Metrication matters is an online metrication newsletter for those actively involved, and for those with an interest in metrication matters. You can read all previous issues at Metrication matters newsletter when you scroll own to the bottom of the page. Go to Metrication matters for the latest revised version of the Metrication matters home page.
Editorial
The "metric conversion" process and it has never been shown to be effective during a change to the metric system. Here is how the Australian Metrication Board viewed the "metric conversion" issue
The learning and use of conversion factors was strongly discouraged because it required people to have a good memory for figures and be good at mental arithmetic. Further, continued use of conversion factors kept that person firmly tied to imperial benchmarks and effectively prevented the establishment of similar benchmarks in metric numbers.
Because I write that metric conversion doesn't work I am often accused of hating "metric conversion". My response usually goes something like this:
"I don't "hate" metric conversion. I am simply an interested bystander who observes when others choose to go down the "metric conversion" path. After extensive study I am convinced that "metric conversion" never works, never has worked, and, in my opinion, metric conversion never will work.
I also know from experience that a metrication program using "direct metrication" can be done in a single day. If you choose "metric conversion" for your metrication process, you should sit back, put your feet up, and wait for the "metric conversion" process to run its course (say 200 years) before you then decide to change your approach to "direct metrication" and then do your metrication process in a single day.
Let me give you an example. Suppose you measure pressure for the pumps you make in psi and you want to become internationally competitive. Your first move might be to expand the abbreviation 'psi' to 'pound per square inch', then (ignoring Isaac Newton's 1687 observation that mass and weight are two separate and quite distinctly different things) you next decide that the international "metric conversion" you will use is kilograms per square centimetre.
Firstly, we need to leave aside the fact that your "metric conversion" has no basis in physics or engineering, then we can consider your marketing problem. You have to convince the rest of the world that you are right and that they are wrong — this decision will prove to be intensely frustrating for you and for your clients for years into the future, And it will be very expensive.
An alternative, using "direct metrication", is to

look at the range of pressures you will deal with,

choose the single suitable unit from the International System of Units (SI),

choose a suitable prefix so you predominately need use only one multiple or submultiple of the SI unit,

check that with the prefix you chose you will, almost always, only ever need to deal with whole number. As a result almost all of your staff never use decimals, common or vulgar fractions ever again (Goodbye to thousands of errors and their expensive corrections)
Consider these points:

air pressure varies around 100 kilopascals (lowest ever on Earth 90 kPa, highest ever 110 kPa)

air pressure in outer space is about 0 kilopascals

water pressure at 1 metre in water is about 10 kilopascals

water pressure at 10 metres in water is about 100 kilopascals

water pressure at 100 metres in water is about 1000 kilopascals
Choose to use kilopascals to measure all pressures then you get on with your life – don't look back – and never convert.
Note that scuba divers use a rule of thumb that The actual or absolute pressure at 10 metres is about 200 kPa – 100 kPa from the air and another 100 kPa due to the water.
Scuba divers have to worry about pressure because the pressure exerted by ten meters depth of water is approximately equal to one atmosphere. The scuba divers only care about the pressure from the water not the pressure from the air even though both pressures are present. The two components to the surrounding pressure act on the diver – the atmospheric pressure and the water pressure. A descent of 10 metres in water increases the ambient pressure by approximately the pressure of the atmosphere at sea level. So, a descent from the surface to 10 metres underwater results in a doubling of the pressure on the diver. This is reversed when the scuba diver goes back to the surface. When a scuba diver who breathes at 10 metres and then ascends without exhaling, his or her lungs contain gas at twice atmospheric pressure and this can lead to lifethreatening lung damage.
Notice that from your research you now have some suitable reference points, in this case the pressures at different depths in water, for learning and for training. You could now write your policy postcard (and your training business card) something like this:
We use kilopascals to measure pressure.
We do not use:

pounds per square inch

psi

pascals or megapascals
Here are some reference pressures:

air pressure at sea level is about 100 kilopascals

air pressure in outer space is about 0 kilopascals

water pressure at 1 metre due to the water is about 10 kilopascals

water pressure at 10 metres in water is about 100 kilopascals

water pressure at 100 metres in water is about 1000 kilopascals
Note that these are the pressures exerted by the water by itself. If you want to know the absolute pressures at these levels you have to add the pressure from the air (average at sea levels 100 kPa) to the pressure from the water.
The correct symbol for kilopascal is kPa
For details go to Approaches to metrication.
Note again that I know, from experience and from observation, that "direct metrication" can be done in a single day while, I estimate, that "metric conversion" typically takes 200 years to run its course.
As I said, I don't hate "metric conversion" but it does amuse me to watch otherwise intelligent people thrashing about in the "metric conversion" swamp. As an example, the writers at the Wikipedia pressure page did look back, and the result is best described as a dog's breakfast. I don't like to think about a pressure measurement newbie who found the Wikipedia page when they Googled for "pressure"  they'd still be there thrashing about up to their knees in metric conversion factors  many, many, years later.
Sadly, another example of "thrashing about in the 'metric conversion' swamp" is almost the entire education system in the USA.
2 Feedback  notes and comments from readers
Alan Jamieson wrote to comment on an item in Metrication matters 87.
Pat,
In your editorial of Metrication Matters 87 you cover the subject of 'Freedom of Choice'.
I thought you might be interested in this article from BBC News regarding the resistance of Americans to adopt the dollar coin as a replacement for paper bills.
It has interesting parallels to the resistance to adopting the metric system and shows that allowing 'freedom of choice' can be very costly.
Two statements stand out for me: "Americans are creatures of habit," and "People will grumble and coins will be unpopular for a few months but then they'll get used to it... It's that simple."
Alan Jamieson
3 Oddities  measurements from around the world
Michael Payne, from Virginia is a pilot, and when the roof of an aircraft hangar at Dulles airport collapsed because too much snow fell on its roof Michael was quick to do a calculation like this:

The Dulles hangar is approximately 100 metres by 50 metres.

The snow that fell was 80 centimetres and snow is roughly 10 % of rain, so the equivalent of 8 millimetres of rain fell and was now sitting as snow on the roof.

1 millimetre of rain falling on 1 square metre equals 1 litre of water per square meter of roof.

Given that the density of water is exactly 1 kilogram per litre then for each millimetre of rain there is 1 kilogram per square meter of snow resting on the roof.

The volume of water is obviously 100 x 50 x 8 litres.

The mass of this snow is clearly 100 x 50 x 8 x 1 kilograms.

The overall mass of the snow on the roof is (100 x 50 x 8 x 1) ÷ 1000 = 40 tonnes.
Michael Payne then remarked: "I did not need a calculator."
I repeated Michael's calculations in my head (but then checked them with a calculator). Time taken:

less than 5 seconds for mental arithmetic and

10 seconds for calculator checking.
Working with the coherence of the metric system meant that neither Michael nor I had any need to use Wikipedia or any other reference for things such as conversion factors or density values. Nor did we have any need to fiddle with fractions or to dillydally with decimals.
As a matter of interest, here is the same calculation done using customary measures:
The Dulles hangar is approximately 325 feet by 160 feet. The snow that fell was 2 feet 71/2 inches or 31/7 inches or 1/4 of a foot so the volume of snow is obviously 325 x 160 x 1/4 and, given that the customary density of water is about 62 1/2 pounds per cubic foot, the mass of this snow is clearly 325 x 160 x 1/4 x 62 1/2 pounds and the overall mass of the snow on the roof is (325 x 160 x 1/4 x 62 1/2) ÷ 2000 short tons or (325 x 160 x 1/4 x 62 1/2)/2000 short tons (Use 2240 pounds for long tons). I used Wikipedia as the reference for these figures and I will leave the final calculations for your amusement.
Never to let an opportunity pass, I was then inspired by another thought from Michael Payne that the transition from Roman numerals to customary measures was an improvement as significant as the change from customary measures to the metric system. I couldn't help myself, so here is the Dulles roof calculation done in Roman numerals:
The Dulles hangar is approximately CD Roman feet by CC Roman feet. The snow that fell was II•• Roman feet plus so the volume of snow is obviously CD x CC x II•• and, given that the density of water in Rome is about XLV libra per cubic Roman foot, the mass of this snow is clearly CD x CC x II•• x XLV and the overall mass of the snow on the roof is (CD x CC x II•• x XLV) ÷ MM Roman tunna. I used Wikipedia as the reference for these figures and, again, I will leave the final calculation for your amusement.
If you are like a challenge I would appreciate it if you keep track of the time it took you to complete the calculations in conventional measures, and then in Roman numerals. Please let me know your times so I can report back to Metrication matters newsletter readers.
4 Tips  pointers and methods to make your measurements easier
To get a rough idea of how much light there is in a candela you could just light any ordinary candle; even something like a small candle to use on a cake will do. As a matter of interest, an early French measure of light was called a carcel and this was the amount of light equivalent to 10 candles.
5 Signs of the times
You can think of mountains higher than 1000 metres as super mountains. At least this is the way they do it in the UK. See Super Mountains for details.
6 Quotations
We must become the change we want to see.
Mahatma Gandhi
7 Q&A  readers' questions and answers
Question:
I have been reading a science fiction book, 'Brasyl' by Ian McDonald, where a French speaker said: "The Amazon drops only fifty toises over its entire length". Can you tell me what is a toise?
Answer:
A toise is a measure of about two metres. It arises from the outstretched arms of an adult male when you measure from fingertip to fingertip with his arms stretched out horizontally.
When I measured my toise it was 1900 millimetres and I will remember this as a 'handy' guide for estimation when I am doing repairs on the house or moving furniture.
8 Rule of thumb
The Sun at the centre of our solar system is an average size star. In fact, as stars go, it is a star that is really unimpressive compared to other stars in the Universe. However, even though it is only an average star the Sun releases more than 300 yottajoules of energy every second (300 YJ/s). As you possibly know, 'yotta' is the highest prefix in the metric system and is equivalent to a number that begins with a 1 and is followed by 24 zeroes.
9 History
Everyday, I see the word, 'barrel' bandied about in the media. This was especially so during the oil disaster in the Gulf of Mexico.
Some years ago I had the good fortune to visit the Permian Basin Petroleum Museum in Midland, Texas, where I discovered that no 'barrel' had ever existed for the collection, storage, marketing, buying, or selling of oil.
Nevertheless, this has not stopped journalists creating stories like this heating oil in barrels story where you will notice that the 'barrel' for oil was always a theoretical concept.
However, I was intrigued by the last paragraph where the writer said:
... the US will continue using its own special measurement for the foreseeable future, despite the obvious benefits of adopting the rest of the world’s established standard.
By the way, you can approximate the nonexistent oil 'barrel' as 159 litres. For example, if the current price of crude oil is quoted as $100 USD then this means that the price of crude oil is about 63 cents per litre. I can then compare this with the local fuel price of about $1.39 per litre.
10 Hidden metric
Because the inch has varied so much over the years there have been many attempts to standardise its length. One definition, from 1814, reads, "three grains of sound ripe barley being taken out the middle of the ear, well dried, and laid end to end in a row". See Wikipedia Inch for details.
Since 1814, there have been many different definitions for the inch but these days most people use the metric inch of 25.4 millimetres as defined for English speaking countries in 1959.
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.
Pat is the author of the ebook, Metrication Leaders Guide.
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