For the system at hand one would measure the reading at, say, position 1, and at position 2 - two extreme points.
The difference between the measurements is the precision on can achieve.
For example, if at position 0 you measure Rp of 3000, and at position 10cm you measure Rp 23000, then you get 20000 codes for 10cm, and your resolution is 10cm/20000 = 5um.
Of course, you, then, have to consider the noise present in the system, and whether you can or not average some of it out.