Don,
I used the 10 mile calibration technique and gave the Speedometershop.com (United Speedometer Service) my numbers and they sent me the adapter within a week. I am completely satisfied (1/2% off).
The technique at the top of the page in your link suggests a 1-mile measured mile. Luckily, when you call them, they ask for a 10-mile measurement. I averaged 4 ten-mile measurements.
I saw the Jim Carter adapter right after I bought mine. Most likely I would have tried to save $$$ and bought from Jim Carter - and I would have been bummed out.
Tim
