These days most photographers barely think of using a light meter as everything is built-in to their camera. However, until the 1970s few cameras had a light meter, so hand-held devices were commonplace.
My father’s was a Gossen Sixon selenium device made in “Germany (West)” which I suspect means that it was a fairly early one from the mid-1950s.
They sell for less than £10 on eBay.
There’s one in the Science Museum: Sixon Exposure Meter and Case | Science Museum Group Collection
The English instructions can be found here: www.pdfcameramanuals.com.
Gossen, the original manufacturer, still have the manual on their website: ba_sixtomat_d.pdf