You needto determine what normal film speed and development times are for you r combination of film+developer+agitation+water supply. Only you can do that !

Start with the normal ISO and development times as recommended my the manufactur er. If you then follow the procedures laid out in "The Zone VI Workshop" book by Fred Picker you will be able to determine what will be for you are the "real" f ilm speed and development times.

Once you have established your "normals" You can then apply the factors that Jef f suggested above.

Ansel Adams was a great photographer and an excellent innovator and teacher, but sometimes in the translation from field to classroom to paper the lessons gets way bogged down.