The Model 3820 Universal Counter allows up to eight measurement outputs to be generated as a function of time, these being: Frequency Average period Average duty cycle Average pulse-high time Average pulse-low time Event counts Logic level (input voltage above/below threshold) Time The counter is principally intended for counting bi-level signals, which have two distinct voltage levels and clean transitions between them. Such signals include those generated by all common logic families used in electronic circuits, as well as most Trigger or Sync outputs of common test instruments. Measurements are updated at one of five user selectable intervals in the range 5 ms to 100 ms. the module is powered and controlled directly from the PCÕs USB port, so requires no additional power source. Operation is entirely via software, with no manual switches or settings.