通过从文本文件中读取所选值,从下拉菜单中保留所选值

I have the following code that allows the user to put the Timing Status on either On or Off

<html>
<?php
if (isset($_POST['Submit1'])) 
{
    $TimingStat=$_POST['timestat'];
    $fileName = 'test.txt';

    $lines = file($fileName);
    $lines[0]="Timing_status= ". $TimingStat;

    file_put_contents($fileName, implode($lines));
    fclose( $fileName);

}
else
{
    $TimingStat=explode(" ",$lines[0]);
    $TimingStat=$TimingStat[1];
}
?>

  <form action="test.php" name="Calculation" method="post">  

    Timing Status: &nbsp;<select selected="selected" name="timestat"   VALUE="<?PHP print $TimingStat ; ?>">

<?php $attr= 'selected="selected"'; ?>

 <option VALUE="On"  <?php echo  $TimingStat == 'On' ? $attr : ''; ?>>On</option>

 <option VALUE="Off"  <?php echo  $TimingStat== 'Off' ? $attr : ''; ?>>Off</option>

</select>

<Input Type = "Submit" Name = "Submit1" Value = "Save Parameters">
 </form>

 </html>

It is important for me that the values be written in a text file and then the code reads from a text file.

Everything works fine, except when I refresh my page the selected value will always go to On although Off has been pressed. Any help would be appreciated. Thank you