From the book by Roger Hicks and Frances Schultz: The authors state that a friend of theirs, who is renowned for the quality of his prints, just develops films in the developer recommended by the manufacturer and using the method and time recommended by the manufacturer, and starts testing by rating the film at the recommended speed. If the first roll comes out under-exposed, he just rates the film at 2/3 of the speed used previously, leaving the development time unchanged. It sounds nice.(posted 9079 days ago)If you have the impression that your negatives are too hard or too soft, but the speed is fine (i.e. the shadows still show some detail), change the development time. If the contrast is too low, try 5% more development, if it seems too high, try 5% less. Repeat as necessary.
There are plenty of other methods, some relying on extensive test-target shooting and printing, others on the use of a densitometer (the latter being the fastest methods, but also the most expensive). Yet: If your speed settings for a film works for you, and the negatives print well on a medium grade, you are already in the ball park. Never touch a running system unless you expect considerable improvement!
All the fuss about the "correct" speed and gradient is only justified if you can measure the exposure and contrast to sufficient accuracy. If you only use an averaging wide-angle meter, there is, in my opinion, not much to be gained by sophisitcated calibrating.
The most important thing about calibrating is that you get familiar with the material and methods you use, and that you keep them constant.