this seems highly unscientific?
Each zone has a inches/hour setting for how much water falls. That times the area gives the volume of water dispersed. Reasonably scientific, I think.
The problem comes with how do you figure out the inches/hour number. Catch cups work. Sprinkler heads often give you that value but they presume a particular line pressure and as well often have adjustment screws that change things.
I think everyone runs into this at the start. IMHO the device should MAKE you give it the sq footage. I doubt that 1000 sq ft is actually right for very many zones. But of course the more you make the user do the less "friendly" the initial setup.
So the recommendation is set out catch cups and run the zone for a few minutes and see what they catch. (I use three and take an average.) Convert that to inches/hour. Also measure (at least closely estimate) the area of the zone. As to drips, I don't know a good way to get the inches/hour. I just went with what the drip head said. I also use 1 sq ft per drip.
It might be nice to simply measure the water flow while you are watering, but that is not a simple task for me.