consider the running_pct as a running total down the list of results..

The top row returned will be the same.. then running pct is that value plus the next largest as you go down..

So

WaitType ----- Time ----- PCT ----- running_PCT

Wait 1 ------------------- 50 --------- 50

Wait 2 ------------------- 40 --------- 90

Wait 3 ------------------- 5 --------- 95

etc

Hope this helps.. 😀