Start with 10% less, it's easier math. The film is still in constant contact with the chemicals during the rotation, they are streaming down the sides. It would have to be intermittent rotation for them to not be constantly bathed.
Even when developed to the same relative density I find that the negatives from a rotation method have a different look than those done with intermittent or stand development.
Yes, agreed... there would still be chemicals on the film. And 10% is much easier.. haha
In what way does it look different? Better or worse or just different??
Here's what I got from the "updated" Jobo instructions...
A five minute pre-rinse of any black and white film works with the developer to produce a negative with manageable contrast and good tonal range, using the manufacturer's recommended 'hand process' (intermittent agitation) times. To pre-rinse, put a quantity of process temperature water in the tank, equal to, or slightly greater than, the amount of developer. Allow this loaded tank to rotate on the processor for five minutes. At the end of that period, pour out the pre-rinse water, and pour in the developer. Pre-Rinse times shorter than five minutes may produce irregular development, and should be avoided.
If you do not want to use a pre-rinse, you will need to determine the appropriate developer time for each specific situation. Rotary agitation affects different film and developer/dilution combinations to differing extents. Some developing times may be essentially the same, while others are significantly shortened or even extended. As a rough guide, try shortening the developer time by about 15%. This could vary by anywhere from about -25% to +10% from the original 'hand process' (intermittent agitation) times. A five minute 'pre-warm' is recommended when foregoing the pre-rinse. This time allows the film, reel(s), and tank to stabilize at the development temperature, before the developing begins.