grid type example corrected

doc/manual.tex

@@ -6979,7 +6979,7 @@ information.
 \end{eqnarray*}
 \end{itemize}
 
-Table~\ref{utc} shows a small example of a grid of natural numbers using
+Table~\ref{utc} shows a small example of a grid of strings using
 this syntax, where there are two levels and only one node in each
 level. A larger example using a different type (\verb|%sG|) is the following.
 \begin{verbatim}