I want to make sure I understand this technique. I am reading information from this website.
From what I can understand, you have it set up like a galvanic cell, but in the middle of the wire connecting the electrodes you have a voltmeter which measures the current (converting it to potential? using V=IR?) but doesn't let any through to the other electrode so no reaction can happen. So the electrons at one electrode can still sense the potential difference between them but the voltmeter blocks them from travelling all the way through the wire? The potential you get is proportional to the concentration of analyte you are measuring according to the Nernst equation.
Please let me know if what I have said is correct or if I have misunderstood.