[AJ]

They use a wideband. Assuming you are in the car while it's on the dyno (Pass seat) you should have time ot make an adjustment if it's quick before the next pull. Usually people will try a change in boost or something small, no extra time for tuning. It's a great chance to see where you are at to get things start and see how you have got you're car set up before setting up some time to do tuning for an hour or so with one of the shops.