Open Location Android app - Feedback wanted!

Hello all! I created an Android app to help me with a project (a reverse geocaching box). Basically I had a Bluetooth shield but nothing with GPS. I also wasn't sure if the Arduino could handle the math involved with calculating geographic distances. But I knew my Android phone could. So I created "Open Location" for my own purposes. You enter a desired lat/lon and radius. When you get within the radius of the lat/lon coordinates I simply send a different character over Bluetooth serial to my Arduino device. More detail on the site, but looking for feedback on the app. Realize this my first Android app and I am mostly a hardware guy so the app ain't pretty! Thanks! https://play.google.com/store/apps/details?id=appinventor.ai_mbparks.OpenLocation2

Basically looking to see if this "proof of concept" app could be rewritten to provide real value.