The NL601 has a digital counter which produces an analogue output proportional to the count. A pulse at the input socket increments the counter towards a full scale count of 255, 2550 or 25500 which is selectable by the front panel scale switch. The counter will continue to increment on input pulses until the unit is reset. This can be done manually (with the on, off/reset switch) or by applying a pulse to the reset socket. Alternatively, with the unit set to internal-reset, when the counter reaches full scale the unit will automatically reset.