The 33500U-OCX adds a high stability time base to the 1 and 2 channel 33500B series waveform generators, giving them a stability of 0.1 ppm, more than 20 times higher than the standard time base in a year.
This option is available for the following models: 33509B, 33510B, 33511B, 33512B, 33519B, 33520B, 33521B, 33522B
With optional arbitrary waveform generation, the Keysight (formerly Agilent) 33500U function generator provides powerful basic function and waveform generation capabilities at a lower price. It provides standard waveforms as well as pulse and arbitrary waveforms (optional), and is the most stable function generator in its class with low frequency and distortion.