Using a manual light meter to determine the aperture of your camera may take some getting used to, but once you become accustomed to how your meter works, you should be able to get readings without much difficulty. Manual light meters allow you to read the reflected light of your subject or the incident light in order to properly gauge your exposure.
Locate the ISO setting on your manual light meter. Adjust the ISO setting to match the film speed in your camera.
If you are shooting a landscape or something at a distance, you will measure the reflected light of your subject.
Point the white ball at the centre of your subject. Press and release the needle lock button. Read the number closest to where the needle has been locked down.
Match the needle reading number to the appropriate number on the exposure dial. Read your aperture exposure from the aligned dial.
Set your camera's aperture to match the aperture reading from your light meter.
Measure the incidental light of your subject. If you're shooting something at close range, for instance a portrait, you may choose to measure the incidental light of your subject.
Remove the white ball for reading reflective light that covers the light reading disc.
Position the light meter at the centre of your subject with the light reading disc pointing away from your subject. Press and release the needle lock button. Note the number closest to the needle position.
Repeat Step 3 from each side of your subject. Match the needle reading number from each reading with the appropriate number on the exposure dial.
Find the median exposure of the various incidental readings you took. Set the camera aperture to match the light meter reading.
Bracketing your photographs by take multiple exposures at the aperture above and below your reading can help guarantee an accurate exposure.