The Smartline controller uses real-time, on site weather information from the Smartline Weather Stations (SLW1 and SLW5 or SLW15) to calculate the daily ETo and apply that to the programming in auto adjust to accurately calculate the run times for each individual zones that is needed to replace the water that was lost that day.
Most people don't know their latitude. That is why we designed Smartline to ask for your zip code – so we code find out your latitude. Why latitude? Based on the date programmed, the controller knows the historical solar radiation levels for that latitude. Why historical? The earth has rotated on a well defined pattern for about the past 4.54 billion years, so there is very little change to this number. In fact, the most stable number in the equation is solar radiation. Temperature, wind, and humidity can always change from year to year, but in July the N Hemisphere is always tilted toward the sun and tilted away in winter. So, that is why we ask for Zip Code for your Smartline controller.