This one is for Android
https://play.google.com/store/apps/details?id=uk.co.eastcourtmanor.sourdough&hl=en
This one is for iPhone
https://itunes.apple.com/gb/app/sourdough-calculator/id463352431?mt=8
I use the one for iPhone quite a bit , comes in very handy.
Not sure if the Android one is for Phone or Tablet and I do not know if the iPhone one also works on iPads.