After using my Gen 1 for nearly two seasons and actively following and participating on this post I think that we actually need two different items:
1. PR as it's currently programmed, don't change anything. Users would use catch cups to accurately measure the amount of water hitting their lawn and Rachio uses this value to compute watering times as it currently does.
2. Actual water usage. Users would input actual GPM per zone by reading their water meter and Rachio would show total water used for watering based on the input GPM and the amount of time the system watered for. This item would not be used for any watering calculations, purely information.
The problem I'm having is that I've got a lot of poorly designed zones, for example a small (~100 ft2) zone with 6 heads that in total run about 10 gpm. When I run the hand calc to back out PR I get a huge, unrealistic number (due to the poor design a lot of the water misses the grass, very narrow, long strip) If I then use this number for zone PR I've gotten the usage data on Rachio very close to exactly matching my actual water meter usage, however, because the PR is so high the algorithm spits out ridiculously low watering times which I then have to adjust. I know I can play with the efficiency setting but it takes a lot of time to go back and forth making small changes, creating new schedules, etc. just to see that the adjustment on the scale wasn't enough or was too much.
If you input actual PR via catch cup test and actual flow rate per zone, in theory Rachio could accurately calculate correct watering times without having to guess at efficiency so much as well as accurately calculate the amount of water used. You could even 'guilt' people into fixing their inefficient systems, for example: "Your watering cycle today used 868 gallons of water, 502 gallons went into you lawn and 366 went to the street/sidewalk and then down the drain, based on water prices in your area you put $X down the drain"...
Just a quick thought... It seems like I can get good calculated watering times OR accurate usage information using the information in this post but I've yet to find a way to get both. Simply adding an input for GPM in place of PR will not solve that problem.