Android is coming, it's in review with Google since yesterday. I haven't been able to test on any actual Android device so who knows, it might work.
The rock bottom section at the top shows what goes into the rock bottom gas volume. You can configure your SAC rate (of course) and the times and SAC multipliers for the various stages. By default it starts with four minutes at depth at four times SAC (two excited divers troubleshooting), ascent at the usual rate at four times SAC and a safety stop at two times SAC. This isn't entirely precise of course as part of the ascent is above the safety stop and perhaps should have a lower SAC, but it's minor. Since you can set the times in question you can remove the safety stop (zero minutes) if you don't want it as part of your calculation. Or lower the SAC multipliers if you want the calculation to apply to just yourself and not yourself plus a buddy, or whatever.
The above rock bottom gas volume then becomes the rock bottom pressure for each cylinder ("RB"). The gas time is the time at your normal SAC at the configured depth until you reach the rock bottom pressure figured from above.
For me, as a newbie switching around between different kinds of tanks, this has been useful in getting a feeling for what to expect in gas time and how much to keep in reserve with some sort of scientific basis behind it. OW rec only though, of course.
Some of us (at least me) would be happy to test out the app a little before Google "approves" it? If you want to share before it hits the shelves....