I don't know of many professionals that are willing to babysit an irrigation system so that the lawn gets water, "as needed"...
The best that can be done is to figure out how much water/time it takes to soak up the root zone for this individual lawn... then ,,, depending on weather conditions,,, see how long it takes to become dry again as turfmd101, suggests...
That's all the math necessary for a perfect lawn... too much water becuz of lots of rain??? shut off the irrigation until it is showing drought or the soil actually dries enough to get air in the structure again...
This business about "Irrigation Formula" is just another money making scheme to remove
common sense from watering, "As needed"...
