Thanks Renee, we keep tinkering with it. Maybe we will get the magic number soon!

It is the tire circumference that is off on mine. We have tried to get them lined up and are off by about .50 for a 20 mile ride. My average speed is slightly lower. Overall, it gives me a pretty close measurement. I just want it perfect. My poor husband has tried to figure out the math at least 3 times.