CLLocation speed

I am developing GPS application. Do you know about how to detect speed of mobile device ?

Actually, I need to detect the speed every 2 seconds.

I know didUpdateToLocation method is called when location changed.

- (void)locationManager:(CLLocationManager *)manager
    didUpdateToLocation:(CLLocation *)newLocation
           fromLocation:(CLLocation *)oldLocation

But I think this method is not suitable for my issue.

So, Do I need to check speed of [CLLocationManager location] in 2 seconds ?

Any suggestion ?

Thanks in advance.