Any tips for calibrating distance on Unltragauge?

I just got my Ultragauge from the group buy here on TW and this thing is cool. The directions say to calibrate the distance on the gauge and then says to drive between two mile markers at 50+ mph to calibrate. I hope somebody has done this before and can offer some tips. I live in Va. close to I-95 and it would seem a little dangerous to pull over on the shoulder at a mile marker and then drive for 3+ miles and then pull over to calibrate. Any ideas?

 

I did mine at night. Little to no traffic. It just takes a second to pull over, stop, clear and drive. Do it when it is safe. I went five miles until it was safe to pull over at the next available marker.

I did find my truck was running 2-3 mph (indicated on speedo) higher than actual speed when I was above 50mph.