It is not a surprise to find some hum for the high resistance values. Normally the high Ohms ranges should use relatively high voltage ranges. Here this seem to be the 2 V range. It may take some shielding to get good readings.

The voltage range could go up to 2V, it's current generator of (around) 200nA

For the 10 M range 4 wire Ohms measurement does not make much sense.

I think you're right :

- Right because it's a nonsense to mesure high resistance value.

But I need to add something I'm thinking :

- Using a 4-wire cables it's possible to use shielded cables and differential input (for sense wires) for a more precise measurement.

But I could be wrong with this, I'm not sure (never tested, never simulated...)

I've also notice a strange math simplification inside the original software :

You could write :

f1(x) = 1/(1/x)

f2(x) = x

It's okay to say f1(x) = f2(x)

But it's false for a CPU !

Original Siglent Software uses a function like f1(x) that could cause a "divide by zero". But without simplifying the function, it's possible to avoid the "divide by zero" like f2(x). I don't understand why Siglent have done this...