My car is going about 50 mph on a highway.

My speedometer and HUD are malfunctioning. Any ideas?  You can see the HUD (heads-up display) just below the car traveling in front of mine...it is reading from 0 mph up to like 50mph at any given time.

Both the speedometer and HUD fluctuate in sync with one another. My engine isn't showing any signs of being affected, ie it still runs smoothly...