There's a three month trial period http://onlinelevitra.in.net/ levitra 20 mg "Of course, those aircraft are not out there all the time, they have an 8-hour work day just like us," he said. "Plus, it's dangerous." But the relative low cost of the GPS method -- the signals are read through a receiver chip -- allows meteorologists to basically run the model non-stop, thereby providing more data to the modeling systems.