How do I calibrate the outside temperature reading on my 1998 Volvo S70?

My 1998 Volvo S70 displays the outdoor temperature, but it is off anywhere from 5-25 degrees. How can I calibrate/recalibrate this feature so it is half-way useful?|||The only time the outside temperature reading is valid is when the car is moving. Because of the location of the sensors you will never get a good reading when the car is at rest or moving slowly. As far as I know there is no way to calibrate them. There are two sensors that read the temperature and you get the best guess of the reading.