Ron Koczor:
I read with interest the article about the gravity Probe B on the following web page:
http://science.nasa.gov/headlines/y2004/26apr_gpbtech.htm?list533332
I understand from that page that you are the responsible NASA official for this article.
It was a fascinating story about an experiment that I had been following for some time. It was marred, however, by the awkward use of a mish-mash of measurements, some in the SI metric system, some in older versions of metric system and even some in Ye Olde English mixture.
I would be interested to know how much of the complex mix of units was a result of the scientists and engineers who actually use those measurements and how much was the result of the reporting and editing of the information for this article.
Of particular concern was the use of the unit "micro-gauss". The SI unit of magnetic field is the tesla. A gauss corresponds to one-ten-thousandth of a tesla.* In SI, the field of "3 micro-gauss" could have been given as 0.3 nanotesla. The use of an SI prefix (like micro) with a non-SI unit (like "gauss") is odd (although not entirely unheard of) but the use of a hyphen between them is something which definitely is not done in SI metric and which I have never seen it done by anyone else in any other system of units.
There really was no need to use all those Olde English measures. Most of the people who are sufficiently interested in reading this type of article would be reasonably familiar with the SI metric system which is used so extensively in science. The reference to 400 miles could have been 650 kilometres, the 1.5 inches could have been 38 millimetres, the 12 feet could have been 3.6 metres and the 400 gallons could have been 1500 L (or 1.5 cubic metres). Few readers would have any trouble understanding those measures and many would prefer them.
It is curious to note that when a good SI unit, the nanometre, was used, it was "explained" by telling that it is one-millionth of a millimetre. The author apparently knew that the reader would understand how big a millimetre was so it could be used to explain the nanometre. So why did the author have to give the diameters of those spheres in inches; if the reader understands millimetres in the other case, surely he or she would understand 39 millimetres in this case.
There was very little other information reported in SI metric. Temperatures in kelvins and the SI related degrees Celsius were the only other metric uses. I would have thought NASA reports on scientific work would have been reported using the units that are almost universally used by scientists; SI metric. I am disappointed to find that this is not so.
Sincerely, Dr. William Hooper Prof. of Physics (ret.) University of Virginia's College at Wise
* I recognize that the magnetic field measured in CGS units of gauss and the magnetic field measured in the SI units of tesla, are not the same thing. Therefore, the tesla cannot strictly speaking be said to "equal" a number of gauss. The problem here is a bit more fundamental; namely, why are NASA scientists still using the definitions of quantities (as well as the units) of the old CGS system instead of using SI and the definitions of quantities inherent in that system.
