ah so the meter is not coupled to the manual controls. at least it still functions in manual though. seems like that is rare.
The nice thing about the Ricoh500G is that in manual mode the meter is coupled to the shutter speed, so as you change shutter speeds the meter points to the appropriate F stop in the viewfinder. If you want to expose at a particular aperture then you just move the shutter speed ring until the needle points to your chosen aperture.