[downeaster]

I am always bemused when I see or hear a "professional" give advice on lawn irrigation times. My lawn service guy leaves a note telling me how long and how often I am to irrigate. A master gardener included a chart of watering times in a recent issue of the VHA "Villages Voice". They give this advice having no idea of the extent of my system.
They do not know the size of my spray nozzles. My Hunter rotaries come with twelve interchangeable nozzles ranging from 0.7 GPM to 12.7GPM @ 50 PSI.
They don't know how far they spray. The range of these Hunters are 22 to 52feet. The range is reduced by containing the distance without reducing the GPH flow.By setting back the range you increase the coverage per square inch.
They don't know area they cover. My rotaries cover from 90 degrees to 180 degrees on the same zone. Assuming the same size nozzles and same range, the 90 degree head will deliver twice the coverage per square foot as the 180degree head.
They don't know the layout. My system was installed prior to my purchase. It was very well laid out so the heads cover from head to head.
They don't know my type of soil. In fact, my soil varies from one area to another. Sandy to loamy to clay.
I have been managing a St. Augustine lawns ( four different homes) for 29 years. I have found the only way to calibrate my sprinklers is to use a rain gauge at numerous places around the lawn. I also watch for spots that show distress too soon (it usually means it needs more water). I adjust times and change nozzles as indicated.
It takes a while but it is worth the effort.
Don't mean to preach but some of my neighbors have had their lawns ruined by following the advice of so-called experts.