Q:  Suppose that our measurement of the distance <b>d</b> to a star
          happens to be in error by 5 percent.  What is the resulting
          error in the radius of the star?



          Since the relationship between our computed radius R of a star 
          and its assumed distance d is linear

 
                 R   =   d   sqrt ( flux / sigma * T^4 )


          then an error in distance of 5 percent will produce an error
          in stellar radius of 5 percent as well.