Followup :

For the Foma 100 (rated at 50, in Pyrocat-HD 1:1:100, time escapes me as my notes are elsewhere right now), I've been using the following formula for the reciprocity and it has been pretty good...

Time_new = (Time_old+1)^1.25 - 1 where "^" means "raise to the power of", probably the y_superscript_x key on most calculators.

This is Mr. Schwartzchild's formula with p=0.8

Perhaps too much information for most pinholer's but then I just tend to get a little silly with this stuff.