You measure discharge times repeatedly ensuring the capacitor is never fully charged. Presuming you know the impedance, temperature and charge voltage you can g

You measure discharge times repeatedly ensuring the capacitor is never fully charged. Presuming you know the impedance, temperature and charge voltage you can get very precise. It's a frequency counter after all. Distance control is sort of weak which is why these are no good against vibration. Another way is to use contact resistance with very accurate bridge temperature corrected voltmeter. More expensive. Essentially a potentiometer. Dimensionality is less important, but contact still is. To do that you need a high-ish impedance wiper you can slide over.