I used Applied Ballistics before I got Strelok Pro. I still have AB on my phone, but never use it. AB is not half as intuitive as Strelok Pro.
I run Strelok Pro on my mobile, tablet and Windows laptop (using Bluestack). I keep Strelok backed up to a free copy of Dropbox and restore to whichever device I'm using.
At some point I will buy Strelok Pro from the Galaxy Store to get the very latest version.
Regards
JCS
