Yes, zero field is zero field whatever happens 
There is still plenty of work to do to fully characterize it, and plenty of potential causes of drift: the ADC, the field dependence on temperature, the mechanical stability of the microscope stage among others. I imagine the actuators will need to be calibrated at least once, depending on all these factors, but that is simply a case of making the scan and doing the fit. If it seems this will become part of the project then I’ll write some scripts to do that.
I really need help putting the modified actuator back into the full model. Any volunteers?