Here in southwest Florida, most lawn types are irrigated based upon so many inches of water per week. So I also agree the best parameter for us to be able to set is the rainfall based upon the average of the last 7 days. It may have rained 2 inches today (typical in the summer) and then in three days, I do not need to irrigate again as I have far exceed my Empire Zoysia requirement of 1 inch per week. If the formula only looks at today and yesterday, our typical 1-2 inches of rain every few days will still allow Opensprinkler to run.