Voltage contrast enables potentials and potential distributions to be observed in the SEM. Its origin is due to the low energy secondary electrons gaining or losing energy as the emission point potential is lowered below or raised above earth. This contrast is enhanced using pulsing and lock-in techniques and is used in the qualitative inspection of devices. Linearization by secondary energy analysis allows voltage measurements to be performed in the SEM. Various methods of linearization are in principle identical. Quantitative estimates of the minimum detectable voltage change with these techniques have also been obtained. The low bandwidth limitations of these measurement schemes may be overcome by using sampling techniques. The sampling SEM demonstrates that voltage waveforms to 100pS risetimes may be resolved with a voltage uncertainty of less than 100mV.