The Doomo Meter D is a small, light accessory meter that serves well for people who use older Leicas and similar rangefinder cameras. The meter conveniently slips into the camera's shoe (adjustable palcement of hotshoe mount ) while readings are taken. Three dials - one for ISO, one for aperture and one for shutter speed allow settings to be made.A series of LEDs illuminate to tell the user when correct measurement has been achieved.