Heading Reference Line and Scale
A white scale on a grey background moves in front of a fixed yellow reference line to show the actual magnetic heading. "TRU" will be displayed when the display shows true heading and not magnetic heading. This occurs when the latitude is above 73 degrees north or below 60 degrees south.
Selected Heading or Track Index
Displayed with a blue triangle. This pointer displays the heading or track displayed on the FCU. If the heading selected is outside the range of the scale, the value of the selected heading is displayed in numbers on either the left or the right side of the scale. If the flight director push-button switch is off, a second heading or track symbol appears on the horizon line and markers are displayed every 10 degrees.
Actual Track Symbol
This is a small green diamond that displays the aircraft's actual track. It is underneath the selected heading or track index. This takes into account any crosswinds that is changing the aircraft's track.
The track of the aircraft is not the same as the heading. Heading is referring to the direction the aircraft is pointed at whereas track is referring to the actual direction of the aircraft travelling across the ground. This can be affected by things such as crosswinds.