Davis has posted new blog update in July 09 2019.
You can see the blog update at www.davisinstruments.com/blog/meteorology-101-understanding-indexes/
Take a short excerpt paragraph below.
Meteorology 101: Understanding Indexes
“Your Vantage Pro2 or Vantage Vue gives you more than just raw weather data. While raw data is very useful, our systems offer several indexes that can increase your understanding of what that data means if you happen to be, you know, a human being. They can tell you what you want to know in terms of your comfort in the current conditions.”