Show how to re-enable GC during timings.
diff --git a/Doc/lib/libtimeit.tex b/Doc/lib/libtimeit.tex
index 98c1c83..1c4e05b 100644
--- a/Doc/lib/libtimeit.tex
+++ b/Doc/lib/libtimeit.tex
@@ -82,6 +82,18 @@
times through the loop, defaulting to one million. The main
statement, the setup statement and the timer function to be used are
passed to the constructor.
+
+\begin{notice}
+By default, \method{timeit()} temporarily turns off garbage collection
+during the timing. The advantage of this approach is that it makes
+independent timings more comparable. This disadvantage is that GC
+may be an important component of the performance of the function being
+measured. If so, GC can be re-enabled as the first statement in the
+\var{setup} string. For example:
+\begin{verbatim}
+ timeit.Timer('for i in xrange(10): oct(i)', 'gc.enable()').timeit()
+\end{verbatim}
+\end{notice}
\end{methoddesc}