Does the interval you're measuring move around much? Can the measurement system touch or be affixed to it? Sounds like a pair of nice calipers might work. So

Does the interval you're measuring move around much? Can the measurement system touch or be affixed to it? Sounds like a pair of nice calipers might work. So depending on your precision needs, you might get away with the same approach: sliding grid of capacitive cells that slide over the measurement cells. Microcontroller measures them as it slides through. Atan2() for the final result. The meter only part of this is called a DRO(Digital ReadOut)