I've not heard of any way to calibrate the speed display.

I measured by car at freeway speeds (70 Mph) and I came up with an error between 5 and 6% fast with OEM wheels and tires. I've included this on my software fix "wish list" that I sent to the factory, but I'm not holding my breath that it will be addressed.

The real shame is that with the digital speed readout, there's absolutely no reason why this can't be fixed in the software. It's not like they've got to drive a motor to turn a needle (like in the Gallardo).