Measuring caps in the single digit picofarad range isn't easy! Most multimeters with a cap tester don't go down that far. The Fluke we had at RIT didn't either.
Here's what I came up with: As oscillator based on a 555 timer IC. Add a specific capacitance and you would receive a specific frequency. We did have a good frequency counter!
So here's how it worked: The pf sized caps were placed in parallel with a known larger cap we knew was stable and produced a specific frequency.
A frequency chart was made for known good values of single digit and small double-digit value picofarad capacitors in parallel with something like a .1uf capacitor. I can't remember right now what the large cap's exact value was.
You HAVE to use something like an english terminal strip for this project! No long leads going to the capacitor interface. Everything has to be rigid- no moving wires. The circuit has to use very good components and have a very good, ripple free power supply. The better you make it, the better she'll perform!
