I totally agree with Boris on this.
I asked the same thing and was basically told to use the provided formula like a good little boy. I have a rose garden with a 1-gallon / hr emitter on each bush. Since I know that I’d like to give them a gallon of water I just set the system for an hour. Still, my gallons used estimate is all messed up since I know that the system only used 20 gallons.
I don’t see how hard this can be to program. For crying out loud, I’m walking around with a computer in my pocket that’s more powerful that the first desktop I ever owned. So again, I agree with Boris, give me the option to put in the number of emitters and their flow rate in gallons per hour.