Which brings up a whole other debate. To me, either Wind Speed data is important or it isn't. Am I right? If it's an important factor than why does the Hunter unit by itself not account for wind speed at all? Why do you have to buy an OPTIONAL $450 unit to complete the E.T. calculation? It's like Hunter is saying, "Well, you don't really need wind speed data. But if you think it's important, we will offer you this expensive upgrade...." Huh? It's either an important part of the formula, or it isn't. At least with Rain Bird, they already made up their mind. They decided they wanted the full equation and that wind speed was an important part of that equation. Then the question was how best to deliver accurate wind speed into the formula in an economical way that keeps the price point low enough that most homeowners will go for it? I guess a few of the options were; 1) Add an anemometer, adding greatly to the expense 2) Get the data over the air from a local weather station, like the E.T. manager does (which bears it's own expense) or 3) Use historical average wind speeds per month. There may be other choices they were considering, I have no idea. That's just what I could come up with off the top of my head. So they did some testing and found that #3 could actually get the E.T. equation pretty darn close to accurate and cost relatively nothing compared to the other 2 options, so they went with that. At least they made a firm decision on the matter and that part of the equation is included.