Hey, this is the app I use for Android! Great job, I use it every time I fill up to mix.
As far as octane calculation...that's such a shot in the dark. People should stop using what octane the pump (or the internet) tells you and just log so you know how much boost and timing to run.
Everything will always work out on paper. NOT everything works out in the real world

2018 Audi RS3 | APR Stage 1 E85 and 91 Flashes | JB4 for Logging
SOLD: 2017 F36 440i Gran Coupe | PS2 | MPPSK | Track Handling Package | JB4
SOLD: 2007 E90 335i | PS2's | JB4 | FBO | 160k+ miles on the car, 120k+ miles on the JB4
Log, log, then log some more...