How do you use a light meter for your camera?

The selenium photometer is the best as this does not require external batteries but uses a photoelectric cell. This is funneled through various resistances and shunts and displays on an analog meter numbers called EV- exposure values. Meter cycles left to right. One sets on a dial the film speed being used ( before any photo session) I use ASA 400 , and then turns the superimposed analog dials to line the needles up- and reads off the exposure values in F-stops and shutter speeds- usually- and this is the nice touch- there is more than one possible combination. In effect a form of circular slide rule. This modern type of photometer ( a term serious shutterbugs prefer to Light meter- as it is used for Photography)- was essentially perfected as far back as l947. It is moderately compact, can fit in a normal pocket, and uses Photovoltaic ( which generate their own juice) cells, unlilke the Cadmium cells which require an external voltaic battery to provide juice- the Cadmium Photometers alter the resistance- thus need outside juice, the Seleniums generate their own- lower maintenance costs. They are hard to get but useful and scientific items! The Slide Rule Museums has a series of patent diagrams on photometers of the wheel-dial or analog type- of which I am familiar. Properly maintained these things hold up.