Example: RSI Ballistic calculator calculates that at sea level in 59 degree air and 29.53 BP a bullet with a .540 BC at 2700 FPS zeroed at 300 yards will drop 307.9" at 1000 yards. The same program, same BP, bullet, velocity, zero, temprature, but change the altitude to 5000' and the bullet drop is calculated to be 315.8 with the same barometric pressure imput. The differance is 7.9" I always thought that the actual pressure and not altitude changed the bullets perfomance. I know pressure changes with higher/lower altitudes go hand in hand, but thought that altitude in and of itself had no effect on the bullet and just the pressure change with the altitude. Any ideas?? Is the RSI program correct or is it a glitch?