The Trek® 520 voltmeters are not your typical hand-held field-meter. Their measurement technology provides surface voltage measurements that are essentially independent of the sensor probe-to-measured surface spacing. The Trek® 520 is available in two versions: 520-1 and 520-2. The Trek® 520-1 has a digital meter to display the measured voltage. On the other hand, the Trek® 520-2 has an analog output monitor in addition to the digital display. This analog output monitor can be used to record the measured voltage or to view it on an oscilloscope.