<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>
