You mentioned in a YouTube comment about measuring the voltage drop across a 1 Gohm resistor using a 10 Gohm impedance voltmeter, but I didn't understand your answer. Normally we would expect the voltmeter to bypass some current around the resistor and affect the voltage reading (by about 10% or so?), but you said this would not be a problem. I could only understand this not being a problem if the voltage was buffered in some way using an even higher impedance sensor, but then why would you need to remark about the voltmeter being >10 Gohm impedance? Please would you explain this in more detail?