Shoot a test roll of an evenly lit, featureless wall. Expose alternatingly at -4 stops from the meter reading and at +3, for a seven-stop difference. Cut a piece from this roll, long enough that you get at least one plus-exposed and one minus-exposed frame. Develop, using your best guess for a time.
When the snippet is dry, measure the relative densities of the two frames by putting it on a light table (or other evenly underlit surface) and putting a light meter with the sensor in contact with the film, and taking a reading. I made a small snoot for the sensor on my Sekonic L308B meter. Otherwise, you can use a camera's built-in meter, if you create a mask with a cutout for the film, then place it over the lens.
The difference between meter readings from the two frames should be 4 stops*. If it's more, develop another snippet at a shorter development time and measure again. If it's less than 4 stops, increase your time.
This is the equivalent of using a densitometer. It's more accurate and faster than lighting a full-scale subject and printing the resulting negative.
Note that the -4 exposure should show a bit more than shadow of density compared to no exposure (it should actually be 1/3 stop over base density, but that can be tough to measure). If there's no density at all in the -4 frame, you may need to lower your EI and shoot another roll. However, if there's a lack of density and the contrast range is low, first increase your development time and process another snippet - it may be that there's insufficient -4 density because of gross underdevelopment.
*4 stops times 0.3 log = density of 1.2, nominally appropriate for diffuser enlargers. I've started developing to a range of 1.1 instead, finding that my current papers don't need that much contrast. That corresponds to range of 3 2/3 stops.
Otherwise you won't see the difference between wet and dry parts.
