So far it seems that the errors that each GPS gets are independent of each other. At about a foot apart our Due calculates the approximate distance between the two is anywhere between 9m and 90m which makes no sense. Worse case scenario is that they should read about 20m apart assuming each GPS has 10m accuracy and each is assumed to be right next to each other at first reading then eventually drifts to the farthest part away of its accuracy.