如何在提交时跳转到锚点 - 而不是返回页首

Question

在这个页面上，我有一个怀孕计算器脚本：http://taranakimidwife.co.nz/index.php？ ...... Itemid = 104

目前，计算是按页面跳回到顶部。我想要它去锚#pregcalc。明白我的意思了吗？这是脚本：

---

<?php
<?php if(!empty($_POST['calculator_ok'])):
   //last cycle date
   $date="$_POST[dateyear]-$_POST[datemonth]-$_POST[dateday]";

   //convert to time
   $lasttime=mktime(0,0,0,$_POST['datemonth'],$_POST['dateday'],$_POST['dateyear']);

    // next period start
    $next_period=$lasttime + $_POST['days']*24*3600;
    $next_period=date("F d, Y",$next_period);

   //first fertile day
   $firstdaytime=$lasttime + $_POST['days']*24*3600 - 16*24*3600;
   $firstday=date("F d, Y",$firstdaytime);

   //last fertile day
   $lastdaytime=$lasttime + $_POST['days']*24*3600 - 12*24*3600;
   $lastday=date("F d, Y",$lastdaytime);

   //have to adjust due date?
   $diff=$_POST['days'] - 28;

   //due date $date + 280 days
   $duedatetime=$lasttime + 280*24*3600 + $diff*24*3600;
   $duedate=date("F d, Y",$duedatetime);

   ?>
   <div class="calculator_table">
   <p>Here are the results based on the information you provided:</p>
    <!-- <p>Your next <b>menstrual period</b> is expected to start on <strong><?php echo $next_period?></strong>.</p> -->
   <!--<p>You next <b>most fertile</b> period is <strong><?php echo $firstday?> to <?php echo $lastday?></strong>.</p> -->
   <p>Your estimated <b>due date</b> is <strong><?php echo $duedate?></strong>.</p>
   <p align="center"><input type="button" value="Calculate again!" onclick="window.location='http://<?php echo $_SERVER['HTTP_HOST'];?><?php echo $_SERVER['REQUEST_URI']?>'"></p>
   </div>
<?php else:
   //the calculator comes here
   ?>
   <div class="calculator_table">
   <form method="post">
     <p>Please select the first day of your last menstrual period:</p>
   <p><?php echo date_chooser("date",date("Y-m-d"))?></p>
   <p>Usual number of days in your period: <select name="days">
   <?php
   for($i=20;$i<=45;$i++)
   {
      if($i==28) $selected='selected="true"';
      else $selected='';
      echo "<option $selected value='$i'>$i</option>";
   }
   ?>
   </select></p>
   <p align="center"><input type="submit" name="calculator_ok" value="Calculate"></p>
   </form>
   </div>
<?php endif;

//to print a date chooser - get name and value in mysql date format
function date_chooser($name,$value="")
{
   $months=array('','January','February','March','April','May','June','July','August',
   'September','October','November','December');

   if(empty($value)) $value=date("Y-m-d");

   $parts=explode("-",$value);

   $day=$parts[2]+0;
   $month=$parts[1]+0;
   $year=$parts[0];

   $chooser="";

   $chooser.="<select name='".$name."month'>";
   for($i=1;$i<=12;$i++)
   {
      if($i==$month) $selected='selected="true"';
      else $selected='';
      $chooser.="<option $selected value='$i'>$months[$i]</option>";
   }
   $chooser.="</select> / ";

   $chooser.="<select name='".$name."day'>";
   for($i=1;$i<=31;$i++)
   {
      if($i==$day) $selected='selected';
      else $selected='';
      $chooser.="<option $selected value='$i'>$i</option>";
   }
   $chooser.="</select> / ";

   $chooser.="<select name='".$name."year'>";
   for($i=(date("Y")-1);$i<=2050;$i++)
   {
      if($i==$year) $selected='selected';
      else $selected='';
      $chooser.="<option $selected>$i</option>";
   }
   $chooser.="</select> ";   

   return $chooser;
}
?>