The meter is intended for use in extreme low light conditions. It attaches to the camera's accessory shoe and connects, via a cable, to the camera's meter cell, the Booster increases the sensitivity of the CdS circuit in the camera and does not, itself, contain a CdS cell. It is compatible with Canon FT series and Pellix cameras, a switch on the top of the meter switches between models, it is used in stop-down mode.