== Clarifications - April 2009 == 

 I have made some tidy-ups in the article, to make a clearer distinction between the concepts of "voltage" and "electric (i.e. electrostatic) potential".  In doing so, I have removed the "Radio Shack" reference, on the grounds that it is 30 years old and superfluous - as we already have a direct link to the most up-to-date official international reference source to SI units. (  )(Richard)