Weather Radar tilt calibration
The tilt indicated on the ND comes from the selection made on weather radar control panel. The value of tilt indicated on ND is not taken from any tilt sensor located on the antenna assembly.The actual tilt of the antenna could differ from the control panel selection because of various attitudes of the air planes and due to various forces acting on the antenna assembly during flight.
When do calibration of the tilt on ground in maintenance according to Maintenance manual , aircraft roll and pitch are non existent and forces acting on the antenna during flight are also non existent.So when do calibration on ground it may show correct tilt as per weather radar control panel but in flight it could differ.Normally the weather radar manufacturers take these factors into account to see the difference is not very much.
For practical use for ground mapping,one may tilt the antenna in manual mode from control panel so that you can get the required return signal.