Okay. I've had time to run only one experiment, using M-Plan 0.98.2. I turned off *all* of the optional conservatism, including gradient stops. I first found a schedule for two dives using nitrox that gave a 2 minute deco stop for each, so if the gas loading changed I would see the results in the deco stop times. M-Plan will generate a minimum 1 minute stop. Here's the schedule: 130 ft 15 minutes EAN28 -> stop at 10 ft for 2 minutes 0 ft 60 minutes AIR 80 ft 60 minutes EAN36 -> stop at 10 ft for 2 minutes I then changed only the gas for the first dive, to 28/25. Here is the result: 130 ft 15 minutes 28/25 -> stop at 10 ft for 3 minutes 0 ft 60 minutes AIR 80 ft 60 minutes EAN28 -> stop at 10 ft for 1 minute So, as far as a straight Buhlmann calculation goes (I don't know how many compartments or the exact model), for this day's diving the helium can be ignored on the second dive. If further experiments of this nature would be of any value, let me know. I'd also appreciate suggested schedules. -- Art Greenberg [log in to unmask]