Zeiss Ikon Ikophot selenium cell light- exposure-meter.
Distinctive lightmeter from Zeiss in Stuttgart
Very easy to use. Set the film speed (eg: 21 DIN / 100 ASA), point the meter at the subject and turn the dial until the pointer with the circle coincides with the meter needle. Then read off the settings for your camera
Never needs a battery. Still accurate afte all these years
Complete with incident light attachment for measuring, er, incident light
As you can see, the Zeiss branding on the outside of the leather case has largely rubbed away - an indication that the meter has been well-used.