I'm trying to show trends using a single value dashboard to compare a count from now and 7 days ago. It seems when I use a one day span and a time frame of 7 days using the xml value <option name="trendInterval">-7d</option> I still get a comparison that counts between the latest data and the previous day. I tried to use a 7 day span instead but that gives me incorrect counts.
index=example | timechart span=1d dc(OfflineDevices) as Offline
Timewrap will be your friend. The app is here, and in its documentation page it has quite a few tips and tricks and how to use it. Try a few of the examples, see if you can modify one to your needs, and if not, please post back and we'll be sure to help!