I've noticed a difference of about 2 mph between the HUD and the speedometer (the speedometer is always faster). Which is more accurate? I'm thinking the HUD because it's probably getting its info from the ECM.

I believe the PCM also controls the speedo.
The speedometer is electronic.

I've always gone under the assumption that a digital readout is going to be more accurate than an analog read...... That's just my thoughts.

You need to find one of those police radar guns that displays your speed. Do your own experiment to see which is closer.

I have found my HUD is the true speed. I have compared mine to a roadside cart mounted radar system.

Analog speedo's used in cars aren't all that accurate due to the method at which the needle moves. Electrical impulses are used to create a magnetic field and this field is what moves the needle plus the printing on the speedo face isn't exactly calibrated to each vehicle. The cost to do that would be outragous in the production of a vehicle. You'll find all cars have an error in the speedo anywhere from 2%-10%. Because the manufacturers no that there will be an error the speedos are designed to read on the high side.

I know my HUD is 1 mph off (+) to actual speed.

I never look at my speedo so I have no idea what it says, for all I know it may not even work.

x2! I love my HUD!

PowerTuner, even more accurate out to the 100th decimal.

I don't look at the speed-o either. Gonna feel weird buying another car without the hud....

X2! However, alot of newer vehicles are coming with digital displays, just not on the windshield, bummer.

My HUD is 2mph faster than the speedo, and I finally found one of those speed trailers that the cops put on the side of the road. The ones that take you pic if you go too fast.

According to that my HUD is correct.

I hear yahs completely. When I get into my truck and work now I always catch myself looking for the hud heh.

I noticed mine today on a 2.5 hour drive, it was Dead on!

wishin' I had an HUD...

I'm wishing for you...