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+<sect2 id="calc-precess">
+<title>Precession module</title>
+<indexterm><primary>Tools</primary>
+<secondary>Astrocalculator</secondary>
+<tertiary>Precession module</tertiary>
+</indexterm>
+
+<screenshot>
+<screeninfo>
+The Precession calculator module
+</screeninfo>
+<mediaobject>
+  <imageobject>
+    <imagedata fileref="calc-precess.png" format="PNG"/>
+  </imageobject>
+  <textobject>
+    <phrase>Precession</phrase>
+  </textobject>
+</mediaobject>
+</screenshot>
+
+<para>
+This module is similar to the <link linkend="calc-apcoords">Apparent 
+Coordinates module</link>, but it only applies the effect of 
+<link linkend="ai-precession">precession</link>, not of nutation or 
+aberration.  
+</para>
+<para>
+To use the module, first enter the input coordinates and their epoch
+in the <guilabel>Original Coordinates</guilabel> section.  You must 
+also fill in the target epoch in the <guilabel>Precessed 
+Coordinates</guilabel> section.  Then, press the 
+<guibutton>Compute</guibutton> button, and the object's 
+coordinates, precessed to the target Epoch, are presented in the 
+<guilabel>Precessed Coordinates</guilabel> section.
+</para>
+</sect2>