But what if there is no velodrome or college running track in your neighborhood, and the Olympics have always passed it by? In that case, dear cyclist in search of precision, you must make your own!

So just how does "The Common Bicyclist" accurately measure out, say 10 miles? The same way the pros do, sort of. First, you need a place to mark your course. You could use an existing running track. A long bike path (or a good sized one that loops) would be even better. But even a smooth quiet (very little traffic) road with few stops will work. You can use the thick sidewalk chalk to mark the start and finish marks. Or, if you want something more permanent, black paint. Just be sure your marks are inconspicuous, and you've made sure it's O.K. to do so (ask). Once you have found a site, you need to measure it. Here's how I made mine.

The best way to do it is to "pace" it off. Meaning walk the course, and measure your distance with a measuring tape of infinite length, namely, your bicycle wheel. In order to do that, you must first get an accurate measurement of the circumference of your wheel, i.e. exactly how far it rolls with each turn, when your walking the bike. I chose the rear wheel is because it follows a much straighter path.

To do this, I took a 30' tape measure, stretched it out to it's full length and layed it on my driveway, locking it so it wouldn't retract. I then walked my bike for four full wheel turns of the rear wheel, and then carefully taped a short machinist's rule (with 1/100" graduations) in the area where the wheel's fourth turn ended (make a fine mark on the side of the tire to go by), lining it's marks up as closely as humanly possible with the tape measure's markings.

I then measured the distance traveled in four wheel turns, recording the exact distance (to the nearest 1/100"). I do this a few times. Averaging the results gave me the rolling distance accurate to within about 0.0003" for each wheel revolution.

Which is certainly close enough.

I then took this distance and divided it into 633,600 (the number of inches in ten miles). This gave me the number of turns the rear wheel will make in that distance, plus any left over fraction of a wheel turn. This fractional amount I multipled by the wheel circumference to get the remaining distance in inches, which I will measure off after all the necessary wheel turns.

Next, I took a piece of cardboard, and using a clothspin, attached it to the valve stem of my rear tire, folding it so it "clicked" against the stays, signaling each turn. But any reliable means of counting wheel turns will do. Then armed with a counter, chalk or a small can of paint, measuring tape and a calculator, I began marking my calibration course.

First, I made a small line with the number "0" at the starting spot. Placing my rear wheel on it, with the "clicker" just just past it's "click", I began walking, counting each click along the way. When I had reached the requisite number of clicks (wheel turns), I stopped, and using the tape measure, added the remainding few inches. Here I marked another line with the number 10.00. To be sure of my measurement, I re-paced the course. In my case there was only a 6 inch difference difference between the two measurements. If you get a wheel turn or more difference, start again, you obviously miscounted somewhere.

Having made sure that the course was accurate, I measured 52.8' before and 52.8' past the finish line, marking these 9.99 and 10.01 respectively. So when testing my computer's setting, a reading of ten miles anywhere between them would mean it was accurate to at least 99.9%

How accurate is my "calibration course"? Well, figuring the initial error of ±0.0003" in the wheel circumference, times the over 7700 turns that wheel made in the 10 miles gives me a total error of about ±2.34" overall, or an accuracy <<>99.999%. Even when figuring in innaccuracies in the pacing out of the course, caused by not holding a perfectly straight line, bumps, gravel, etc. it should still be more than accurate enough achieve a bike computer's 99.9%.

Now that you have your very own calibration course, learn how to use it by clicking here!