This view finder fits onto the accessory clip (often referred to as flash shoe these days) and has two settings, 35 and 80, to match the focal lengths of the extra lenses. When set to 85 the parts of the photo not captured by the lens are blanked out.
The knob on the rear has both feet and meters scale. Once you have focused using the camera integrated range finder you turn this scale knob to the appropriate position and the viewfinder is tilted so that parallax is corrected.
A neat small leather pouch is available to protect viewer when not in use.
Small light meter for IIc and IIC. I think it better to use a hand held Weston V or Euromaster. Note the white cover for incident light readings. Also note the large selenium cell which does not require any batteries. Again there is a bespoke leather pouch to protect meter when it is not attached to the camera.