Thank you. I understand now, and I also understand what @brianflynn was trying to explain so I've give him the 'Correct Answer' because he got there first (thanks Brian).
I'm presuming therefore that a more meaningful chart to show the progress (or not) that we are making in addressing slow-running queries would be the Top Waits trend chart, which is more the shape I would expect - we've made some progress in addressing some of our worst-performing queries, but we still have some way to go.
Richard
