Understanding how potentiometry works

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.

• Yes that is the gist. The half cell potential depends on the concentration of the ion as given by the the Nernst equation. A high impedance voltmeter is used to measure the voltage. "High impedance" means that virtually no current flows. Virtually in turn refers to the concentration of the ion at the surface of the electrode. If a "lot" of current is flowing then the concentration of the ion is depleted at the electrode compared to the bulk of the solution, so the EMF drops as the current increases. – MaxW Nov 13 '15 at 21:35