Don't know about calibration, but these are electronic speedometers with electrically operated mechanical odometers, so they should be accurate internally. Mine does, however, have the gauge needle attached at the wrong angle, so it reads about 2 mph fast at all speeds. Sounds like you have the same problem, but the other way.
Removing and reinstalling the needle is a process though. The needle has a stop at 0, and the servo behind it does not. IIRC, you have to take the Speedo out, turn the needle to the right until it points straight down by itself, gently pull it off, press it back on at the correct angle (straight down, but adjusted from the angle it was at by the amount you noticed it being off), then you turn in back to the left until it rests against the 0 stop. There's also a high probability of breaking the needle in the process.
I just live with mine being off because I don't want to risk breaking it or making it worse.
I missed this post. Honda's speedometers do read on the high side. I first noticed it when I had tried a GPS unit in my car for a couple of days, and wondered why the GPS unit was incorrect. I later learned (from another CR-V forum) that the speedometers read on the high side. Even my '09 was doing this. The only "adjustment" is to change tire sizes. I figured that my speedometer was reading about 2.5% to 3% high. On my '97, I ended up using 205/75R15 tires and that pretty much corrected it and on my '09, I went with 235/65R17 (as opposed to the OE 225/65R17) and that has corrected it. (I didn't change the tire size for that reason, but it is a nice added bonus.) I'm pretty sure our Civic reads on the high side also-- our Acura TL did.
GPS is actually fairly accurate, at least in the handful of phones I have used. I've compared GPS, radar and speedometers numerous times, and have in most cases found the GPS and radar to be pretty much the same, where the speedometers in the handful of Hondas I have owned have read about 3% over.
I have an app called Ulysse Speedometer on one of my Pixel phones, which makes for an easy comparison.