The PM 6669 is an economic, easy-to-use counter that meets your most stringent demands for high-precision measurements, reliability and durability. The multi-function PM 6669 offers frequency, period, count totalization, ratios, pulsewidth and frequency difference measurements. Available options for further enhanced functionality include a 1.3 GHz input, battery pack and high-stability MTCXO timebase oscillator plus an IEEE-488 bus interface. option PM9606/011 Rack Kit for PM 6666 PM9606/021 Rack Kit for two counters or for PM 6666 and 8840A/42A PM9604 GPIB interface PM9607/001 MTCXO Time Base PM9581/011 50 O feed through termination 3W PM9585/011 50 Ohm Feedthrough Termination, 1W PM9608/201 1.3 GHz HF-Input