Designed to fit into a broad spectrum of applications, this trio of timer/counters range from the low-priced Model 900 with a 250-ps single-shot time interval resolution to the Model 901 having a 50-ps resolution and the high-cost Model 901R equipped with an atomic Rubidium timebase frequency reference. Other features of Model 900 timer/counter include a 225-MHz basic frequency range and a speed of 2000 measurements/s. By comparison, Model 901, which is closely related to the 900, boasts of of a speed of up to 8000 measurements/s and a frequency range that can be extended from 300 MHz to 2.7 GHz.The most sophisticated meter of the three is Model 901R. It is said to offer outstanding accuracy when used for frequency calibration, with uncertainty pegged at 0.0001 ppm. And its warm-up time is also said to be very short.