Zero Point

Anything you want as long as you always use the same point. I use driveshaft movement.

 

zero

while not exactly the same, the consensus point for most Top Alcohol tuners is when the flow meter goes up. Some start when the flow meter and pump pressure intersect. Some look for the drop in fuel pressure. Some go off of boost going up. Most are basing around the WOT event in a foot swap. Two step and air throttle launches may need to go off of either clutch switch or transbrake switch event.

If you are comparing notes or getting advise from someone and they say you need x amount at .25 and this much at .5, etc., you need to know what they zero off of, because if you go off one of the above methods and compare it to someone who is going off of driveshaft, it's comparing apples to oranges.

Like Mike said, find whatever works for you and stick with it.