Google Trends has been a popular tool since its launch in 2006. It is one of several free tools that provides some helpful insight into search query popularity and by extension search volumes (although the tool doesn’t explicitly report on search volumes). Since launch Google has added features, such as “hot trends” and country/city where the search queries originate.
Now Google is adding a relative “numeric scale” to Trends and downloadable CSV files.
Here’s a search for “hd dvd, blu-ray” before:
The numeric scale is on the vertical (Y) axis. According to Google, “these numbers don’t actually refer to exact search volume figures; instead, Trends scales the first entered term so that its average search traffic in the chosen time period is 1.00. Then, each additional term is scaled relative to the first.”
Here’s more information and color from the Google Blog.