The frequency standard 6689 is equipped with a highly stable quartz oscillator (OCXO, oven-controlled crystal oscillator). It was specially designed for use in test systems for telecommunications or in calibration laboratories, where particularly fast and economical calibration of several devices such as e.g. B. frequency counter and synthesizer is required. The frequency standard 6689-021 is equipped with five additional 10 MHz outputs and thus offers a frequency output of 10 x 10 MHz and 1 x 5 MHz.