Thanks Ian. I've just checked if there is any data on the Foma Bohemia site - lazy me - and they do list the time for Perceptol but they don't mention at what exposure when it's obvious from the graphs on the second page of the document that only Microphen and Xtol can reach the speed of ISO 100 at gamma 0.6.
Well, the Massive Dev Chart suggests 7:30 at EI 50 or 8:00 at EI 100 for Perceptol stock; 10-11 minutes 1+1, EI 100; 14-15 minutes 1+3, EI 100. That should provide some starting points---it seems sort of optimistic to target box speed, but you could vary EI through a roll and see what works with those dev times, for a start.
San Diego, CA, USA
The lady of the house has to be a pretty swell sort of person to put up with the annoyance of a photographer.
-The Little Technical Library, _Developing, Printing, And Enlarging_