In Head-Up display, the 12 o'clock position on the PPI represents own ship's course and hence the heading shows zero on the graduated scale around the PPI. All bearings taken on this display will be relative to the heading.
The right side of the heading marker on PPI is the Starboard side of the ship and the left side of the heading marker is the Port side of the ship. If Radar is used in Headup mode while altering the course the Heading marker remains at the same position and the targets start moving on the screen, due to this the picture gets smudged.
Picture smudges in azimuth during alterations of course.
Because of smudging, accurate bearings cannot be taken during large course alterations
Plotting becomes highly inaccurate during yaw in bad weather, as ship's head keeps changing several degrees per second, resulting in severe smudging.