I would use the method Pete Reigel used in the post that Jeff John referenced in the other thread.
http://www.usatf.org/events/co...p?courseID=OH10005PRI did this for a track near me that wasn't coming out correctly in a google earth measurement. It did come out to very close to 400m when I measured it on site with this method.
But you really need to have a measuring wheel, or Rolatape as Pete called it, that measures continuously, as opposed to a wheel that clicks off a meter with each revolution. The latter kind makes it difficult to do an accurate calibration. I bought one online for about $20. It is plastic and cheap, but it gives repeatable results when doing multiple "rides" of a calibration course, and that's all that really matters.
BTW, your calibration course for a measuring wheel does not need to be long because there is no initial wobble.