To visualize and predict the look of an image before exposure it is necessary to know how your film will respond when exposed using your own personal equipment. Here is a test you can do to determine the true speed of your film with your meter, camera and lens.
First, start with an 18% gray card (the Kodak Neutral Test Card is 18% gray which corresponds to zone V of the exposure scale and print value V).
1. Load your chosen film (in 36 exposure length, or 120) into your camera.
2. Place the gray card under constant even illumination, position the camera close enough to the card to fill the frame with gray and focus the lens at infinity. (The infinity focus setting transmits light at full value and will render a featureless area of tone that will record as an even negative density) Use the second full f-stop in the range of apertures on your lens. If it stops down to f16, start with f11.
3. Meter the test surface using the film manufacturers recommended ISO setting and place that reading on step 1 of the zone exposure scale. If the meter indicates f11 at 1/15 second you would set your starting exposure at f11 at 1/250 effectively reducing the exposure by 4 stops to a zone 1 value.
4. Given the above metered value, shoot the following exposure sequence:
1st exp. 1/250 sec. @ f11
2nd exp. 1/250 sec. @ f8
3rd exp. 1/250 @ (halfway between f8 and f11)
4th exp. 1/250 @ f11 again
5th exp. 1/250 @ halfway between f11 and f16
6th exp. 1/250 @ f16
For 35mm users cover the lens and shoot off frames 7, 8 and 9 so they will be blank. Starting with frame 10 repeat the same sequence. Do this twice more to produce four groups of six test exposures with three blank frames in between each group. If you are using 120 film just do one 6 exposure sequence per roll.
In the darkroom remove the 35mm film from the cassette, bring the ends together and cut through the loop in the middle. Double each of the resulting lengths and cut them in half in a similar manner. The blank frames will give you enough leeway to create 4 strips of six exposures. Store 3 of the lengths in a light tight container and process the 4th one in your standard developer using the manufacturers time and temperature recommendations. Fix, wash and dry the film as you normally would. The 3 saved film strips can be used with other developers or if you experience processor errors.