1. Fix the 18% Grey Card to an outside wall. The lighting should be open shade, not direct sunlight... a north facing wall is good. If you frequently shoot film indoors by artificial light use that specific light source indoors for your test.

2. Position your tripod mounted camera loaded with the film type to be tested so as to fill the viewfinder with the Grey Card image without casting a shadow onto it. Focus the lens to infinity (do not focus on the card) to eliminate any extension factor which would not be taken into account using a hand-held meter.

3. Take a close-up reading from the card. Alternatively take an incident light reading from the card's position, preferably using a "flat" rather than the meter's usual "invercone" receptor.

4. With the camera in "manual" mode, and if with a TTL meter, set the ISO rating of the film being tested and make an exposure according to the meter reading. This is your reference shot... an 18% mid-tone Zone V reading and exposure.

5. Stop-down the lens aperture and / or select a faster shutter speed on the camera so that the next exposure is five stops less than the original meter reading. This makes a Zone 0 exposure which should produce a negative having no density except for "film base + fog" often written in textbooks as FB+f.

6. Make a further series of ten exposures... each having one stop more exposure than previously, until you have finally made an exposure five stops more than the first Zone V mid-tone exposure.

Step Wedge
What you have just done is to make a "step-wedge" strip of negatives from Zone 0 to Zone X, which, with the first Zone V reference shot you made will be twelve frames long. This can be cut into two strips of six for convenient measuring, contacting and filing.

7. Expose the rest of the film to either the 18% Grey Card at the recommended meter setting or take normal pictures. This last step is very important because the tone or Zone test film must receive the normal amount of chemical energy during development. A 12-exposure film receives too much chemical energy during development compared to a 36-exposure film processed in the same size tank.

8. For monochrome photographers whose output may total only six films a year the testing exercise stops here. For photographers whose output may be six films a day the test can be continued if necessary by repeating the entire procedure with four more films at 1/3 stop more and 1/3, 2/3 and 1 stop less than the recommended ISO rating.