diff --git a/include/class/anc_operation.class.php b/include/class/anc_operation.class.php
index 49ff5aa44..70dc8f0e8 100644
--- a/include/class/anc_operation.class.php
+++ b/include/class/anc_operation.class.php
@@ -717,16 +717,15 @@ EOF;
         return $result;
     }
     /**
-     * Save the ND VAT with prorata
+     * @brief Save the ND VAT in ANL, and  distribute the amount among ANL Axis proportionnaly to the source
      * 
-     * @param $p_array usually $_POST
-     * @param $p_item item of the form
-     * @param $p_j_id jrnx.j_id concerned writing
-     * @param $p_nd amount nd vat
+     * @param $p_array array usually $_POST
+     * @param $p_item int nb of the item of the form
+     * @param $p_j_id int jrnx.j_id concerned writing
+     * @param $p_nd float amount nd vat
      * @see Anc_Operation::save_form_plan_vat_nd
-     * @return type
      */
-    function save_form_plan_vat_nd($p_array,$p_item,$p_j_id,$p_nd)
+    function save_form_plan_vat_nd($p_array,$p_item,$p_j_id,$p_nd):void
     {
         bcscale(4);
         extract($p_array, EXTR_SKIP);
@@ -787,12 +786,12 @@ EOF;
         {
             $tot=bcadd($tot,$a_Anc_Operation[$i]->oa_amount);
         }
-// utilité ???
-//        if ( $tot != $p_nd && count($a_Anc_Operation) > 0 )
-//        {
-//            $diff=  bcsub($tot, $p_nd);
-//            $a_Anc_Operation[0]->oa_amount=bcsub($a_Anc_Operation[0]->oa_amount,$diff);
-//        }
+        // security : if  tot != nd so the amount is reduced by the difference between computed and max
+        if ( $tot != $p_nd && count($a_Anc_Operation) > 0 )
+        {
+            $diff=  bcsub($tot, $p_nd);
+            $a_Anc_Operation[0]->oa_amount=bcsub($a_Anc_Operation[0]->oa_amount,$diff);
+        }
         for ($i=0;$i<$nb_op;$i++)
         {
             $a_Anc_Operation[$i]->add();