At first I was very pleased with concept I came up with

Since I was about to hookup a scope and a debugger, I made a plan to move the scale instead of the sensor board.

In the CAD world it worked amazing, but in real world we have an issue. The long boards are not flat at all.

This had two side effects, it made sliding of the scale hard and "sticky". And the second and more problematic: we can't keep even gap between the plates. Since the capacitance is directedly effected by space between two electrodes the signal strength varies a lot.

In the caliper I dissected, the T-scale PCB was very thin. At first I thought it would be because it is less material - easy to install and cheaper. Now I find that it has another reason: when it gets glued to the metal chassis it will conform to it and the gap will be maintain. 

With mass produced digital calipers they want to bring the price down as much as possible. They would not do anything unless absolutely needed.  The fact they decided to put his two extra parts (some sort of guards), speaks a lot about the necessity to keep this gap clean and even. 

For the prototype I still find it useful to move the t-scale, but I have to come up with an idea to maintain this gap small and constant. 

Cheer,
M