Air and E.T.'s
keeping records of your run as to what the DA was at the time of the run will help in tracking changes...
a simple air temp...barometer and humidity guage which can be bought from radio shack or wherever...will allow you to do that...then there is software available that you can plug these numbers into that will give you the DA......or you can buy a 400-500 dollar weather station...
make sure you use the absolute barometer pressure...not the one given from the weather station as it is correct...