What is += used for?
<p>I think this is a dumb question but I could not find it on php. Why is a + with the = in the following code:</p>

<pre><code>function calculateRanking()
{
    $created = $this-&gt;getCreated();

    $diff = $this-&gt;getTimeDifference($created, date('F d, Y h:i:s A'));

    $time = $diff['days'] * 24;
    $time += $diff['hours'];
    $time += ($diff['minutes'] / 60);
    $time += (($diff['seconds'] / 60)/60);

    $base = $time + 2;        

    $this-&gt;ranking = ($this-&gt;points - 1) / pow($base, 1.5);

    $this-&gt;save();
}
</code></pre>

<p>Is this so $time has all those values or rather it is adding all the values to $time?</p>

<p>Thanks</p>
