function drawVerticalLine($SeriesName, $Index, $Format="") {
   $VerticalLineR      = isset($Format["VerticalLineR"]) ? $Format["VerticalLineR"] : 0;
   $VerticalLineG      = isset($Format["VerticalLineG"]) ? $Format["VerticalLineG"] : 0;   
   $VerticalLineB      = isset($Format["VerticalLineB"]) ? $Format["VerticalLineB"] : 0;   
   $VerticalLineAlpha   = isset($Format["VerticalLineAlpha"]) ? $Format["VerticalLineAlpha"] : 40;
   $VerticalLineTicks   = isset($Format["VerticalLineTicks"]) ? $Format["VerticalLineTicks"] : 2;

   $Data = $this->DataSet->getData();
   list($XMargin,$XDivs) = $this->scaleGetXSettings();
   if ( $XDivs == 0 ) { $XStep = ($this->GraphAreaX2-$this->GraphAreaX1)/4; } else { $XStep = ($this->GraphAreaX2-$this->GraphAreaX1-$XMargin*2)/$XDivs; }
   $X = $this->GraphAreaX1 + $XMargin + $Index * $XStep;

   $this->drawLine(
      $X,
      $this->GraphAreaY1 + $Data["YMargin"],
      $X,
      $this->GraphAreaY2-$Data["YMargin"],
      array("R"=>$VerticalLineR,"G"=>$VerticalLineG,"B"=>$VerticalLineB,"Alpha"=>$VerticalLineAlpha,"Ticks"=>$VerticalLineTicks)
   );
}

      foreach($this->pChartData->getValues("Date") as $index => $date) {
         $dateSplit = preg_split ('/\./', $date); /* this depends on your format.. mine is DD.MM.YYYY */
         $weekDay = date('N', mktime(0, 0, 0, (int)$dateSplit[1], (int)$dateSplit[0], (int)$dateSplit[2]));

         if ( $weekDay == 5 | $weekDay == 1) {
            $this->pChart->drawVerticalLine("Date", $index, $LabelSettings);
         }
      }