document N_zones_per_right_angle parameter

git-svn-id: http://svn.einsteintoolkit.org/cactus/EinsteinAnalysis/AHFinderDirect/trunk@1026 f88db872-0e4f-0410-b76b-b9085cfa78c5

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+++ b/doc/documentation.tex
@@ -908,6 +908,38 @@ excision.  This feature is controlled by the following parameteters:
 	as registered with the \thorn{SpaceMask} thorn.
 \end{description}
 
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+
+\subsection{Other Parameters}
+
+\begin{description}
+\item[\code{N\_zones\_per\_right\_angle[}$n$\code{]}]
+\mbox{}\\
+	This parameter sets the angular resolution used to compute
+	each patch.  The units are the number of angular grid zones
+	per right angle.  The default is 18, \ie{} a 5~degree angular
+	resolution.  There's no problem with this parameter varying
+	from one horizon to another, but for simplicity it should be
+	even.%%%
+\footnote{%%%
+	 More precisely, it {\em must\/} be even for
+	 any horizon whose patch system type is anything
+	 other than {\tt "full sphere"}.  See the comments
+	 in {\tt param.ccl} for further information.%%%
+	 }%%%
+
+{}	For any horizon which is close to spherical about its
+	local coordinate origin, you can lower this parameter to make
+	\thorn{AHFinderDirect} run faster (typical run-times scale
+	roughly as the cube of this parameter); 6~is about the
+	minimum reasonable value.
+
+	For any horizon which is highly non-spherical about its
+	local coordinate origin, you can raise this parameter to
+	get better resolution; 30~should be enough for even a
+	highly non-spherical horizon.
+\end{description}
+
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 
 \section{Accuracy}