I suspect there are trimmers on the back panel labeled "Zero Trim" and "Cal." The "Zero Trim" is for cases when the "Zero" knob on the front panel drifts off range and you cannot zero it with that knob. (Of course the most likely case is that someone tampered with the "Zero Trim" pot on the back )
The "Cal" trimmer is to adjust the slope of the the response. They recommend a calibrated patch around 2.0 log d in the manual but 3.0, as mentioned by Gregg above is also fine.
In general, the two difficult questions you need to answer are "How much exposure to give" and "How long to develop the film." In the exposure and development process there is no immediate feedback (excluding process-by-inspection), so most folks use a exposure light meter and processing thermometer as guides. The rest of the B&W process can be done in real-time (composition in the viewfinder) or by trial and error in the darkroom.
The practical application of your instrument in solving the two above-mentioned unknowns would be to check for 0.1 log d on film exposure tests of your equipment. This will ensure you make negatives that will print easy.
Second, once you discover, through trial-and-error, a good development time for a film/paper combination, you can use the densitometer to help guess at development times for unknown combinations. The latter is made easier if you are in possession of a sensitometer.
If you have the ability to filter your enlarger light, I'd also recommend printing with multigrade paper and use a single development time for each film/developer combination. This will eliminate hours/days/weeks/months of tedious "N+1," "N+2" etc testing.
Last edited by ic-racer; 04-18-2012 at 01:24 PM. Click to view previous post history.