Originally, just after launch though, the antenna pointing angles were used as a form of input to the tracking data. This trial and error process involved pointing the antennas to various predicted locations, and determining where the best signal was coming from. When that was determined, the investigators noticed exactly where the angles were pointing. Later, when Cassini is farther away, these antenna angles were too rough a measurement to be of any value for tracking. It then became necessary to depend on ranging and the Doppler effect to continually monitor the spacecraft.