Looks like itís a fixed 10mm f/8 lens with 1/100 second and B shutter. It lists multiple exposure capability.
If so, then the exposure for the central area should be about correct at f/16 in sunlight with ASA 100 film.
This translates to a 2-stop overexposure for the central area at the fixed f/8 aperture the lens is equipped with when used under a sunny sky.
In those conditions an ASA 400 film would overexpose the central area by 4 stops.