I thought the lengths of paths would be more precise.
Sorry. But lengths have to be rounded. First, the lengths I get are computed to 4 decimal places. So that is about as accurate as it gets. Before you complain more, for lengths in kilometers, that is to the nearest decimeter (1/10 of a meter). For lengths in miles, that is to roughly the nearest 6 5/16 inches. Considering the lengths of most of what I measure (or anything you measure in GE), is a tiny distance. Don't worry about it.
Now that tool returns english lengths less than 1 mile in yards and metric lengths less than 1 kilometer in meters. In both cases, it once again computes to 4 decimal places. However, that level of accuracy isn't valid. We are talking about to within .1 milimeters or less that 1/20 of a 1/16 of an inch. No matter how accurate the calculations are, the placement of the waypoints in the path isn't that accurate. In fact, I only attempt to put the path or polygon in the middle of the pavement. If we are talking about a runway being used as track (Edmonds or St. Pete come to mind), the width alone could add or subtract 10 meters to the length.