  We report on the influence of voltmeters on measurements of the longitudinal
resistance in the quantum Hall effect regime. We show that for typical input
resistances for standard digital lock-in amplifiers the longitudinal resistance
can show a non-zero minimum which might be mistaken for parallel conduction in
the doping layer. In contrast to a real parallel conduction the effect
disappears when either the current source and ground contact are swapped or the
polarity of the B-field is changed. We discuss the influence of input
capacitances and stray capacitances on the measurement. The data demonstrates
the influence of the voltmeter input impedance on the longitudinal resistance
measurement.
