What is dangerous is that most DBAs have never thought about this. Yet when in a firefighting situation and running interactive scripts, usually very simple queries that gather data once from the underlying performance view are run. The result is a red line query, which can be very misleading.

You can be sure you are running a blue line query if you have a defined beginning and end. You will also notice the values are very dynamic in range, whereas red line values tend to be very static, with little variance.

You're probably wondering if your existing tools and products are reporting the blue line or the red line. The only way to tell for sure is to look at the SQL they are running. The next best thing is to see if there is a defined beginning and ending point. If this is not possible, there is a good chance the tool or product is producing red line statistics. An update button may make no difference. The update button could just keep moving the red line's end point while always using the instance start time as the beginning value.