Me too. But how many times would statisticly be worthwhile? Three maybe? So far I am going to start with shell. I can use the funnel method to be accurate on the amounts used also.
If you had the time, three would be good. Record as much data as possible (temperature, time from start to stop, how much gas used, etc).
I wish there were a way to automate it, but I can't think of a way to do it, UNLESS you set up a video camera and play it back later with the timer to figure out start and stop time.