Just by the way, is it correct to describe an input of a measuring instrument as “floating”? It’s absolutely not a problem for me – I’m just asking out of interest. The input must have *some* impedance, being partially resistive and partially reactive. It may be very high, but it’s not infinite. If the exact characteristics aren’t known, would it then be more accurate to specify some safe minimum (e.g 100M ohm or whatever), and say “> 100Mohms”, plus if the capacitance is known, specify that as well etc etc.

Again – it’s not a problem for me – just asking out of interest to further my understanding.