title: calculating 'timeIntervalSinceNow' with a negative value (CLLocation example)?
body: <p>i don't understand this example from the doc : the <code>timeIntervalSinceNow</code> method should show a positive value, but how can we reach "5" as mentioned in the code? (i think it's either 0 more or less, or -10 , -20, -30 etc... but how can we get a positive value such as 5?) :</p>
  
  <pre><code>- (void)locationManager:(CLLocationManager *)manager didUpdateToLocation:(CLLocation *)newLocation fromLocation:(CLLocation *)oldLocation {
      // test the age of the location measurement to determine if the measurement is cached
      // in most cases you will not want to rely on cached measurements
      NSTimeInterval locationAge = -[newLocation.timestamp timeIntervalSinceNow];
      if (locationAge &gt; 5.0) return;
  </code></pre>
  
  <p>Thanks for your help</p>