To figure the paper contrast to use proceed as follows:
Originally Posted by RichardH
Use the 'white' channel and measure the contrast range from thinnest area of the negative you want detail to the densest portion using the spot probe.
Sometimes it is easier said than done because you may need to move the negative around in the enlarger to minimize cosine falloff which would result if you move the probe around the baseboard. Since it is just an estimate of your printing contrast needs, a little inaccuracies may be tolerated. Once you have your negative range as it is projected on the baseboard, you look up the paper contrast needed in your chart of paper contrast range values you previously made using a contact printed step wedge.
If you measure your negative density range with a densitometer ( not what you have indicated you are going to do), you construct your printing paper lookup table with a projected step wedge.
If you measure your negative density on the baseboard ( as you have indicated you want to do) , you construct your printing paper lookup table with a contact printed step wedge.