Looks to be a selenium cell meter. Originally self powered; no battery needed.

Most of the time the cell has lost its sensitivity due to old age , or its delicate contact areas have corroded.

If working, the meter needle moved in response to the amount of light the cell 'saw' You followed the black or silver band from the meter needle position to a numbered scale, with the scale first set to correspond to the speed of film in use. The film speed might be calibrated in asa, or din values or both.

The meter reading then usually gave you the fastest shutter speed and effective aperture to use for that sensitivity of flim.

You, the user, set the exposure dial and aperture lever or dial to suit that reading, or set it to an equivalent slower shutter and smaller aperture that gives and equivalent exposure.

Hope this helps your comprehension. I have seen a half dozen of these meant for Polariods, etc. None I have seen have ever worked past 1990.