I regularly find myself being worried about whether a design meets requirements for electrical specification or not. One of the parameters is how much a connected device can load a bus, say in the order of 10-400 pF, so that it can be calculated that a total capacitance requirement of all the devices and wires on bus is not exceeded (like 400pF total on open-collector I2C bus with resistive pull-ups).
So do you have a homebrew method that only requires a (good 1 GHz) oscilloscope and some signal generators (HP AWG or even AVR square wave on IO pin) to measure this sub-nanofarad capacitances down to say 10pF with 10pF accuracy so it is known that for example a 50 pF limit per device is not exceeded?
I know there are fancy $5000 capacitance meters that work on multiple frequencies and DC bias voltages but it is so rarely needed and expensive so I won't consider this for my semi-hobby projects.