Add information on mesh size to choose.

21_distributed-memory.tex

@@ -419,7 +419,7 @@ An example is given in Fig. \ref{fig:weak-scaling}:
 \label{fig:weak-scaling}
 \end{figure}
 
-The bounding box scaling controls can be used to create interesting meshes as 
+The bounding box scaling controls can be used to create interesting meshes like
 the $36^d$ cell mesh shown in Fig. \ref{fig:strong-scaling}. This mesh was created with 9 outside cells
 on the left side and 12 ranks per dimension. The mesh
 is interesting since it can be perfectly distributed among
@@ -427,6 +427,8 @@ $2^d$, $4^d$, and $12^d$ processes.
 
 The same mesh refined by a factor $3^i$, $i \leq 1$ can be constructed if $3^i \times 9$ bounding box outside cells
 are placed to the left of the domain.
+The $36^d$ mesh requires a maximum-mesh-size of $\frac{1}{36} \approx 0.03$.
+The uniformly refined variants must scale this mesh size with a factor $\frac{1}{3^i}$.
 
 \begin{figure}[h]
 \begin{center}