My primary calibration course was repaved a couple of years ago. The previous description was from a utility pole at a slight angle. That did not match what I thought was old paint that had extended onto the concrete gutter. So I redid the whole thing. Then, I referenced to TWO expansion joints so as to not rely on the + - 5 degrees of compass accuracy. Only if those two measurements agree, will I have enough confidence to NOT remeasure the whole course.