I have been doing this by slavishly following the manufacturers recommendation of 5 minutes at 1:15 for film rated at 400. Works nicely so far. A few questions though: 1. I have one roll that I rated at 200 instead so I should cut the development time but I am not sure by how much. Any suggestions? 2. How many rolls of 120 can I reasonably expect to develop with one 500ml lot of 1:15 dilution (Paterson tank)? 3. Should I really be increasing the development time by 30s for each subsequent roll as suggested? Looking forward to the usual excellent advice!