The PM6666 and PM6669 are economical, easy-to-use counters that meet the demands for high-precision measurements, reliability and durability. The units use reciprocal frequency counting, which yields high resolution measuring results under all conditions, even on low frequency measurements. The high performance counter frontends, providing variable sensitivity and noise immunity increase measuring accuracy. Accuracy can be further improved with the optional high stability MTCXO TimeBase, that offers a stability of 2 x 10-7 (0°C to 50°C), comparable to that of an oven stabilized oscillator. The counters have high input protection, allowing it to withstand inputs of 12V rms on the optional 50½ RF input and 350V (dc+ac peak) on the 1 M½ LF input. PM 6669 Frequency Counter The multi-function PM 6669 offers next to frequency measurements also period, count totalization, ratios, pulsewidth and frequency difference measurements, functions normally found only in more expensive timer / counters. This counter can be used on the test bench or for field service. It has a full 9-digit display, to allow complete presentation of measuring results. When less accurate measurements are made, blanking of irrelevant display digits makes it easy to read results.