Ron,
Relevant to our recent exchange of ideas on the use of metric in reporting about the Gravity Probe-B spacecraft, I ran across a piece of information that I'd like to mention. In a recent NASA publication I learned that the 400 mile high orbit of GP-B which you reported (and which I had suggested could be identified as a 650 km orbit) is really a 400 NAUTICAL mile orbit (which is closer to a 750 km orbit).
Since our previous discussion centered in part on what units are familiar to your "average reader", I think it is important to realize that most "average readers" are probably even less familiar with the nautical mile than they are with kilometres. Furthermore, instead of two (or three or four*) different kinds of mile, there is only one kilometre so that such confusions don't occur in the SI metric system.
I think your argument that you want to use units familiar to your readers loses its persuasiveness when you use nautical miles (especially when you don't identify them as being the nautical type of miles).
Regards, Bill Hooper
* PS I have found references also to: statute miles, surveyors miles, British miles, Roman miles, international miles, land miles, and my personal favorite the "missizazgoodaza mile". :-)
