The best way to do it is on a road trip. On relatively flat, level highway. Set the cruise on 60 and reset the trip meter. Record the amount of time it takes to go exactly 60 miles, and record the trip odometer reading at mile marker 60. You can then figure out what % off your odometer and speedometer are.
That works if you have a route that you know is accurately 60 miles. If you just look at your odometer...that won't help.
In southern RI on route 95, there's a "measured mile". It has big signs that say "Begin measured mile" and "End meaured mile". If it was a measured 10 miles or 60 miles it would be useful for calibration, but as it stands it's only good for people to see how fast they can complete the measured mile...
Interstates here have mile markers down to a tenth of a mile, for rescue services. I go 50 miles and then use that to calibrate my odometer. The 1 mile mark with a good stopwatch at 60 would calibrate your speedometer.