Tore my tricep completely from where it attaches at the elbow of my dominant arm just 7 weeks before my DIY AK moose hunt this year. Had to have it surgically repaired. Put a stop to all of my work out prep for the hunt and getting all of my "honey-do's" done before hitting the road for 2...
Yes... you can use the app while the animal is on the hoof as long as you can get a picture of it head on using your phone with or without phoneskope. You have to upload the picture to the app to get the measurements.
Not the quickest way but it seems to be very accurate if you have the time.