diff --git a/Doc/Sd1/objectsClasses.xml b/Doc/Sd1/objectsClasses.xml
index cd7d5870a2a572fb4818414526e3e357bf99b694..a6cfabfd1075f2ddb30159f302f1c1137e41e6f3 100644
--- a/Doc/Sd1/objectsClasses.xml
+++ b/Doc/Sd1/objectsClasses.xml
@@ -4184,6 +4184,16 @@ seconds = 23</screen></td>
               created it shall be impossible to alter the instance's values
               <abbrev>i.e.</abbrev> changing its state.</para>
 
+              <para>Supply a so called copy constructor to allow for creating
+              a new instance from an existing one:</para>
+
+              <programlisting language="java">/**
+ *  Clone a given instance.
+ *
+ * @param timeperiod Instance to be cloned.
+ */
+public Timeperiod(final Timeperiod timeperiod) { ... }</programlisting>
+
               <para>Use the following tests to check your
               implementation:</para>