Here is the forumla implemented as it is in the manual:
http://funkja.public.iastate.edu/calculator.php

Code:
<?php
if(isset($_POST['submit']))
{
        $you = $_POST['you'] * 1.0;
        $them = $_POST['them'] * 1.0;
        $hits = $_POST['hits'] * 1.0;

        echo "<strong>Land grabbed:</strong> " . ($them/$you)*($them * .13) * pow(0.7,$hits) . "<br><br>";
}
?>
<form action="calculator.php" method=post>
Your land: <input type=text size=10 name="you" value="<?php if(isset($you)) echo $you; ?>"><br>
Their land: <input type=text size=10 name="them" value="<?php if(isset($them)) echo $them; ?>"><br>
Their Hits: <input type=text size=10 name="hits" value="<?php if(isset($hits)) echo $hits; ?>"><br>
<input type=submit value="Calculate" name=submit>
</form>
I'm pretty sure this cannot be the formula that is implemented in the game - because it is possible to grab more land then they have. Which would be interesting eh?