The frequency standard 6688 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 standard output of 5 x 10 MHz and 1 x 5 MHz can optionally be expanded by five additional 10 MHz outputs.