AeroPod, PowerPod and Newton

When attempting and out and back calibration ride, does the road have to be straight? I'm not sure I can find a straight road where I can ride for five/six minutes. What impact, if any, does a non straight road have on the calibration?

You can ride any kind of road you wish. I do my ride on a one mile loop; I turn around and ride in the opposite direction for the return portion.