Hi gents, I am looking for a ballistic calculator that I can put in the variables-data, get the results and then change 1 data point-velocity and compare the resulting changes.Example, .177, .012BC, 900FPS, 45yard zero, etc. Then change the velocity and only the velocity 25FPS and compare the results.Do any of the free downloadable calculators do this? What is your favorite?I have had a copy of chairgun for years but I could never get it to run on my Win 7 64 bit PC. At any rate, any and all suggestions would be welcome.Thanks, Mike