I am trying to set up a real simple script that allows us to enter a model number in and automatically add 1 to the stock quantity.

We are going to use this with a bar code scanner and as the items come in we will scan each box and want each scan to add 1.

I thought I had this right but it keeps giving me an error..

Can someone please take a look?

Thanks

PHP Code:
<?php
  require('includes/application_top.php');
?>

<HTML>
<HEAD>
<STYLE TYPE="text/css">

</STYLE>
</HEAD>

<BODY>
<FORM METHOD="POST" ACTION="<?php echo $_SERVER['PHP_SELF'];?>">
<INPUT TYPE="text" SIZE=25 NAME="model" />
<BR><BR />
<INPUT TYPE="submit" NAME="submit" VALUE="Submit">
</FORM>

<?php
  mysql_query("UPDATE products SET products_quantity = "products_quantity + 1""
WHERE products_model = $_POST['model']);

?>
</BODY>
</HTML>