Basically: you move the six sliders along the edges to correspond to your aperture and shooting conditions. That moves the exposure slider (which you don’t touch) to the correct shutter speed. There’s an absurdly complex system of internal levers that somehow doesn’t disturb anything other than the exposure slider when you adjust each input.

You can read more about it at https://www.nzeldes.com/HOC/Posographe.htm

I found mine on ebay a while back.