For those interested in the accuracy of their speedometers, try spending the $100 on a gps.
My NSX with the tires I am running seems to be dead accurate. Speedo says 60, GPS said 60, Speedo said 100, GPS said 100, Speedo said 120, GPS said 120. I've gone faster (see my post on page 1), but didn't have the GPS in the car that trip. The radar guns on I-5 up by Shasta Lake have also confirmed the accuracy of the speedo in the 60 to 70 mph range. I don't know if I am just lucky, or if in general Honda made the NSX speedo more accurate than others. My Integra, RL & CR-V are not as accurate. The Integra & RL read high (actual is lower than speedo) and the CR-V reads a little low (actual is a little higher than speedo).