Thanks Paul! Your explanation is very helpful.

So, given the following, are my calculations correct?

- the dial for series resistance on the amp reads 0.3 (= 3 megaohms)

- the compensation dial reads 75%

- the maximal current at one point in time is 6 nA

- the command voltage is to -10 mV

Ru = 3 * 25 / 100 = 0.75 megaohms

Vm = (-10 mV) - (6 nA * 0.75 megaohms)

(after converting everything into volts, amps, and ohms)

Vm = -14.5 mV

And to your point of clarification - I can say then that the maximum voltage error for this experiment is 4.5 mV (since the 6 nA is the maximal current), but not that the voltage error for the entire sweep is 4.5 mV.

Are you saying 4.5 or 14.5 in your clarification point?

If we talk about an inward current (like sodium current in cardiomyocites), should we then put another minus in the equation?

For instance I have a desired voltage of -50 mV and a peak current of -2nA...

Then Vm= (-50mV) - (- 2nA * 2megohms of residual Rs after compensation)

Then Vm= -50- (-4mV) = -46mV

Is this correct?