My worst zone is 108 ft^2, it’s a long narrow piece or grass between the sidewalk and street and the irrigation installer did not design the most efficient zone. Per my meter the zone uses 8.1 gpm, backing out the PR from that gives you 7.2 in/hr which is far higher than what my lawn actually gets measured from catch cups (1.6 in/hr). If I set the PR for this zone to 7.2 the usage information is very accurate, however, the default watering times are way off. They’re too short because the systems uses 7.2 in/hour to calculate the times (among other variables).
Caveat - the above information assumes I don’t mess with the efficiency and leave it at or near 100. You’re right, given the poor design the efficiency is way off. Through trial and error I’ve found the actual efficiency to be closer to 54% and then everything works out.
There are a lot of variables you can play with as you’re all well aware. My whole point is that simply adding a gpm input for more accurate usage data will likely cause you to have to mess with other variables, like efficiency, to get the calculated watering times in the ballpark, depending on your unique system/installation. In my experience it’s a bit time consuming to move the sliders, create new schedules, see how things changed and repeat as necessary. I’d like to input the variables of my yard, as precise as I can measure/determine them, and have the iro spit out ‘good’ numbers (usage, time, frequency). If you use an accurately measured PR for the watering calculations and then a ‘dumb’ usage variable in GPM you could easily get accurate usage information without having to tweak other variables.
Worth noting that it’s very nice that they’ve provided so many tweaks because no two systems are alike and I love the flexibility, just a pain to use.