And update description.

Modelica/Blocks/Math.mo

@@ -2382,8 +2382,8 @@ y = ------------------------
         time - startTime
 </pre></blockquote>
 <p>This can be used to determine the empirical expectation value of a random signal, such as generated by the <a href=\"modelica://Modelica.Blocks.Noise\">Noise</a> blocks.</p>
-<p>The parameter t_eps is used to guard against division by zero (the mean value computation
-starts at &lt;<em>simulation start time</em>&gt; + t_eps and before that time instant y = u).</p>
+<p>The parameter t_eps is used to avoid large fluctuations but can be set to zero (the mean value computation
+starts at &lt;<em>simulation start time</em>&gt; but is only returned after an additional t_eps and before that time instant y = u).</p>
 <p>See also the <a href=\"modelica://Modelica.Blocks.Math.Mean\">Mean</a> block for a sampled implementation.</p>
 
 <p>