I have been using exbal on my palm pilot for the last couple of years for my ballistic calculator for my 338 rum. I have used the program to verify my velocity and calculate my drops and it has worked pretty well. So, I moved up in technology and bought a smart phone and down loaded Shooter. Today I went to the range to get the cob webs off all of my rifles and thought I would refresh my memory with some fresh chronograph readings, so I dusted off my pro-chrono and shot most of my loads through to see if my memory was good. Last year I bought a beta chrono but it seemed to give me faster speeds than the pro chrono and neither seemed to be dead on. So I was using drop charts to verify my velocity. Today the pro chrono was showing 2730 for velocity. This brings me up to my shooting today. 338 rum ,300 grain berger otm, zeroed at 100 yards, 75 degrees, 20% humidity, 4270 elevation, I entered my go to velocity of 2830 and BC of .818 G1 into my exbal program for my 690 yard target and the solution was 15.25 moa, fired and it was on the money. Then I went to my phone and entered all the information into Shooter and it told me 13.2 Then I entered the information into G7 ballistic calculator and it told me 13.7 All of the ending velocities are different. What gives?