I have a 300RUM and Leupold scope with turrets marked for yardage. The yardage is based on 4500' elevation and 40 degrees with 210 Berger VLD's. It has worked well and I have been able to verify the turrets are correctly marked for where I hunt elk each year. I am considering going out of state in search of a big one and most likely that will mean different elevation (higher). Does anyone know of an app for my iphone that would give me the appropriate yardage setting given a true horizontal range and known temp and pressure?