Anticipation

I'm awaiting the arrival of my Ultimaker 3D printer. The printer was shipped before I left for vacation, but was returned by DHL for some reason. It should be on it's way now.

I'm intrigued by some of the objects shown on Dave Durant's blog. I'm already thinking of how to calibrate and tune the machine to be able to do as good as those pieces.

For that, I need a good way to make linear measurements. What sort of home made device can be created to measure repeatability and accuracy of position on the order of 0 to 20cm?

For repeatability I'm thinking of a parallel plate capacitor setup that would convert position to capacitance - which I have a meter for. For a couple of plates with an area of 400 square millimeters (a square 2 centimeters on a side), separated by steps of 0.05 mm (1/16th micro stepping), gives a capacitance of 70.8, 35.4, 23.6, 17.7, etc. picoFarads according to a parallel plate capacitance calculator. So that approach doesn't seem like it would be a good method.