dont rely on electronics, especially an iphone. get a slopedoper or even better a mildot master, get some 550 cord guts and string it in the card and put a 300 win mag case on it, theres a way to get a angle reading. then do the long math, get the angle, take the angle of the slope so say 20 degrees, put it in your calculator, hit COS and get your %. take the COS...say its .98 and multiply it by your range and you will get your horizontal range. use your horizontal range in your ballistic calc, and leave the LOS blank if you can get it to work.