Sexpr problem

Hi.

I am having difficulty  making \Sexpr work as desired.
 Specifically, the pdf and the text  versions of the help system
differ, and I can't reproduce the example on page 63 of
the R Journal article by  Murdoch and Urbanek (Vol 1/2,
December 2009).

Is there an example package that I could examine for Best Practice?

thanks

Robin Hankin
Uncertainty Analyst
hankin.robin at gmail.com