Speaking about 'moving mount Fuji'

I have this device in my office:

Quite a few visitors get baffled what is it. Most are able to quickly figure out that it is some sort of clock since it is 'ticking' (light pattern changes and left side changes slower than the right). However, some couldn't figure out what sort of clock it is and how exactly does it display time. I am seriously thinking about using this as my interview question ;-)