The HP Model 5383A is a direct-counting frequency counter that has a range of 10 Hz to 512 MHz. Nine display digits provide a resolution of one Hz per second for inputs up to 512 MHz. Front panel controls allow a selection of gate times, input impedances, and attenuators. A rear panel connector and associated selector switch allow either an external time base oscillator input, or monitoring of the internal time base oscillator. When the optional temperature compensated crystal oscillator (TCXO) is installed, the rear panel connector serves only as a time base monitor. In addition, a rear panel power selector switch permits the 5383A Counter to operate with line voltages ranging from 90V to 252V (line frequency range: 48 to 440 Hz).