[USMA:28660] Metric in Montgomery Co.

[Bill Hooper]

Mr. Szesze:

Mr. G. Stanley Doore directed me to your excellent metric pages of the Montgomery County Public School web site starting at:
http://www.mcps.k12.md.us/curriculum/science/instr/metric.htm
I applaud your actions to prepare your students for the real world by emphasizing metric measurements in your curriculum.

I hope you will not object to my making a couple comments on the page on unit symbols. My references are to the English version of the official document entitled "The International System of Units (SI)" 7th addition 1998 (and its 2000 supplement when necessary) published by the Bureau International des Poids et Mesures (International Bureau of Weights and Measures).

Under "Mass" I find:
Mg=T = megagram = Tonne (metric)
which is not correct. The SI symbol for tonne is a lower case "t" not a capital "T". (ref: page 105, table 6, "Non-SI units accepted for use with the International System")

The names of the units like tonne (and litre) are not proper names and so should not be capitalized except where you would capitalize other words (such as at the beginning of a sentence or in titles or when all caps are used).

Most people well versed in SI would recommend the spelling "metre" and "litre" rather than "meter" and "liter".

In the various places where exponents are needed, those exponents are not written as superscripts, as they should be. Examples are the symbols for cubic metre and cubic decimetre. Other examples are in the list of all the prefixes. I admit that it is possible that your web page DOES produce the required superscripts and that my web browser just cannot reproduce them.

(I can't produce the superscripts in my email message either, but I would hope that your web page would be sufficiently sophisticated that it could. Either that, or add a note explaining that such exponents should be written as superscripts even though your software is not capable of doing so. I often use the caret mark (^) to indicate exponentiation, thus: m^3 for cubic metres and 10^-6 for ten to the minus 6 power.)

Under SI Base Units, the word length is misspelled, a purely typographical error, apparently.

Under SI Prefixes, I find:
10 -6 micro u
in which the symbol is not correct. The symbol for 10 to the -6 power is the lower case Greek letter mu, not the lower case Latin letter "u". The l.c. mu looks like this � (I hope). I have produce it correctly on my copy of this email message but I cannot guarantee the you will receive it correctly. That is unfortunately the case for a number of special characters when they are transmitted from one computer to another by email or internet.

I am curious about your choice of prefixes to show in your list. It is not complete although it is so long that it appears that you intended it to be complete. It is missing the prefix and symbol for 10 to the plus 24th power, which is yotta (symbol: capital Y). Also missing are the prefixes for 10 to the minus 21st power and 10 to the minus 24th powers. They are zepto (symbol: lower case z) for 10^-21 and yocto (symbol: lower case y) for 10^-24. (Ref: page 103, Table 5, "SI prefixes")

I hope my comments above are helpful. I'm sure you agree that those of us who are responsible for teaching the SI system need to be especially diligent about getting the details correct.

William Hooper
Certified Advanced Metric Specialist