High impedance voltage measuring?

[Artlav]

Let's say you want to measure voltage on an 0.1u capacitor, without affecting it (much).
You touch multimeter probes to it, the display flickers for a moment and reads 0V.
Oops, it's discharged now.

So, how can you do it?
I think something like a buffer on an ultra-low input leakage op-amp might work, but maybe there is a simple trick or tool for this?

[robrenz]

An Electrometer will typically have greater than 100 TOhm input impedance and can easily do this.

[HKJ]

At low voltages some meters can be switched to a high impedance input.

[dannyf]

Oops, it's discharged now.

A 0.1uf capacitor can hold far more charges than what's needed to perform an adc, especially one with high impedance input (like a digital multi-meter).

If the capacitor is of very low value, like in the pf territory, you can either use a low-leakage high impedance converter to buffer it; or rely on charge transfer - only if the meter's own capacitance is known.