When the wire is raised to the potential to be measured, it bends toward one or the other of the blades, depending on the sign. The movements of the wire, which is illuminated by an adjustable mirror attached to the case, are measured with a microscope having an ocular micrometer and, once the instrument has been calibrated, it is possible to arrive at the potential that determined the movement of the wire.
All the connections that can be made with a quadrant electrometer can also be made with this one.