VERY RARE unit. Essential for any high end studio.
Synchronize all your digital gear to the same word clock. This prevents miscellaneous clicks and dropouts in the audio. This prevents time drift from every device using its own independent clock. Say you have 3 different recorders running, this guarantees each sample "clicks" together at the same beat allowing all audio to be perfectly synchronous and not skew or warble.
Can also be connected to an atomic frequency standard for the most precise audio recording and playback possible. This synchronizes the sample rate of your audio gear to an outboard atomic clock!
While it does have that audiophile application, it can also be used to simply sync all digital audio gear. A very unique unit. It also includes an internal oven controlled crystal oscillator for stabilizing extremely accurate recording and playback even without a separate outboard time source. It can be its own very accurate clock too.