In Ted Corbitt's document that Alan directed us towards, the stated accuracy of a surveyor's measuring wheel is 5 yards per mile when pushed slowly ( 2 miles/ hour) and operated carefully, which translates to 0.28%. The accuracy of the bicycle method as we know is better than 0.08% or 4.2 feet per mile between measurements. I was surprised to see the 5 yards per mile number but it's in line with the Keson measuring wheel website that I cited earlier in this thread which states an accuracy of 99.7% (or 0.3% between measurements) on a flat, even track. Many road courses are not flat, even tracks, so presumably the 0.3% for measuring wheels is as good as it gets, particularly if Keson's statement on their website is true that their measuring wheels are "the best in the world".