If I remember correctly, the FORScan instruction for adjusting speedometer for tire changes is it use the needle position for reasons I mentioned in my previous post.
If you set the digital display to 80, you may be one-half a MPH slower or faster. Setting the needle centered to the number you wish to refer to should be correct.
Unfortunately you will have a difficult time learing which is correct but you can settle for which is most accurate to you.

I used 3 GPS devices concurrently when trying to adjust my speedometer, It was almost impossible for 2 of the 4 displays to be the same at any given time. With each varying slightly I basically had to choose which device I thought may be most reliable.
Devices were 2 different portable Garmin devices and my phone with an app. Not sure app matters as they are displaying what the on-board chipset reads (unless I misunderstood how the phone apps function).

 

This is what I found on my 2015 as well. The analog gauge is about 1 mph optimistic at 70 mph.

 

You're saying the digital display is accurate?

 

Yes

 

Hopefully new vehicles will use GPS to determine speed and then all this calibration nonsense will go away.

 

change to a fully digital, problem solved!

 

I never paid attention to the dial. Always the digital readout. Both are the same, now that I checked.

 

On a prior car, I once tested the speedo, v a standalone Garmin GPS, v an iphone speedo app. None of them matched. All differing by 1-2mph

There are so many variables involved in a speed reading that I suggest we focus on more important issues like why the hell do Ford Sunroof equipped vehicles leak when other brands of cars with pano roofs don't.