<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>