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Metrication matters - Number 48 - 2007-05-10

Metrication matters is an on-line metrication newsletter for those actively involved, and for those with an interest in metrication matters.

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Dear Subscriber,


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 metric

1 Feedback

Bill Hooper from Florida wrote to say:

I don't believe that a tablespoon has been adopted everywhere as being equal to 20 mL. I'm not sure it is so defined anywhere except in Australia. Most definitions I've seen are: 1 TBLS = 15 mL and 1 TBLS= 3 tsp.'

Bill is right. There is no international standard for teaspoons or tablespoons; Australia and New Zealand use 5 mL for teaspoons and 20 mL for tablespoons while Canada, the UK, and the USA use 5 mL and 15 mL respectively. Bill then went on to say:

Clearly the teaspoon, tablespoon and cup are not SI units or even approved for use with SI. People and agencies in various fields are free to adopt other special units and to define them in any way they want including defining them in terms of units of the SI system. We may wish they wouldn't, but we can't prevent them. Also, different agencies may define them differently. We wish they wouldn't do that either, but we can't stop them.

I responded to Bill by writing:

By the way, I suspect that the 15 millilitres for a tablespoon chosen by Canada, the UK, and the USA, is simply a soft conversion from the old pre-metric 'half an ounce' (without specifying whether this approximation is an avoirdupois, a fluid, or even a Troy ounce).

And Bill replied:

No, I don't think so. I think it is a simple extension of the old definition that a tablespoon is equal to three teaspoons, so if 1 tsp = 5 mL then 1 TBSP = 15 mL.

2 Editorial

World Metrology Day will be celebrated this year on Sunday 2007 May 20 to commemorate the signing of the Metre Convention on 1875 May 20.

The Metre Convention created the International Bureau of Weights and Measures (BIPM) and set the framework for global collaboration in scientific, industrial, commercial, and societal measurements. This is the third year that the Director of the Bureau International de Poids et Mesures (BIPM) has issued a statement for International Metrology Day. The first paragraph reads:

Open a newspaper or look at the television news, and you can't escape reports on issues related to climate change, global warming, ocean levels and the general state of our environment. It's still to be proven that man is largely responsible for the changes we experience - or think we experience - around us. However, it's clear that measurements have a huge role to play in monitoring change and in providing reliable data for models which predict, or try to explain, the rate of climate change. The theme for the 2007 World Metrology Day is one of the Great Issues of our time - our relationship with our environment.

You can find the rest of this year's statement as it appears in Japan if you go to: http://www.intermet.jp/News/WMD_2007.pdf

You can also find out more about the importance of measurement for global warming discussions by reading the three page pdf article, 'A word about global warming' from /articles.html

3 Oddities

Each year you lose about 4 kilograms of dead skin cells. Most of this becomes dust where you live and work. About 70 % of house and office dust is dead skin cells.

An uncut beard will grow, on average, 150 millimetres per year. You can compare this rate of growth with the length of the beard of Vivian Wheeler who had the world's longest feminine beard at 279 millimetres.

4 Tips

Heady stuff
Since, on a cold day, you can lose up to 70 % of your heat through your head, it is a good idea to wear a well-insulated hat.

5 Signs of the times

Recently, the BBC published a pro-metric article at:


When I read the article there were 149 responses from readers and almost all of them were in favor of the UK 'finishing the job of metrication as soon as possible'. My response is number 144.

Stephen Gallagher from Canada was pleased to see metric distance signs indicating the walking distance from each concourse's underground train station to all the other concourses and the main terminal at Atlanta's Hartsfield-Jackson International Airport. Stephen wrote:

Even better, they rounded the numbers to make them appear more logical; Distance to Concourse A was listed as both 1500 ft. and 460 m (instead of 457.2 m).

6 Quotation

One hopes that each hand will put their best foot forward as, inching towards the goal, they fathom out what yardstick to use to measure the milestones of progress; otherwise, chained by habit to the past, they will have made another rod for their backs, and their flag may never be perched at the pole of the Moon. (Origin unknown)

7 Q&A

Is it OK to use a prefix with litres and with tonnes? That is, is it OK to write megalitre or its symbol ML and is it OK to write megatonne and its symbol Mt?

Not really. One of the essential goals of the International System of Units is to have one unit, and one unit only, for each physical quantity. This means that the SI multiple for 1000 tonnes should go back to the gram as part of the series: gram, kilogram, megagram, gigagram, teragram, and so on. SI discourages the creation of alternate expressions for the same size unit. Hence, if the correct SI unit for 10^12 grams is "teragram" (symbol Tg), no other name or symbol should be used. Specifically, the use of SI prefixes with non-SI units such as litres or tonnes is discouraged. Instead of kilolitres, the equivalent cubic metres should be used. And instead of megatonnes, the equivalent teragrams should be used.

8 Rule of thumb

Aeroplane engineers have to allow for the amount of water that passengers produce as perspiration when they are sitting quietly on a plane. For each passenger the engineers allow for 100 millilitres of water per hour. Your 3 million or 4 million sweat glands can produce up to 12 litres of perspiration in a single day.

9 History

Official investigations carried out in all of China, in 1936, uncovered 53 dimensions for the chi varying from 200 millimetres to 1250 millimetres; 32 dimensions of the cheng, between 500 millilitres and 8 litres; and 36 different tsin ranging from 300 grams to 2500 grams.

10 Hidden metric

Mike Millet passed on an item from the Randolph-Macon College in Virginia that refers to the fact that the penny coin in the USA has a mass of 2.5 grams and a thickness of 1.55 millimetres. It was part of an item that compared the amounts of money in the Federal budget to everyday household items. The item at http://www.rmc.edu/spotlight/2007_budget_numbers.asp included this:

A penny is 1.55 millimeters thick and has a mass of 2.5 grams. Converting the proposed budget to pennies would generate a stack 450 million kilometers high that's three times the distance to the sun. That stack would weigh 800 million tons.


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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