Rich,
You only need to enter weight when you are computing HP. Could never get that to work right. But for 0-60 & 1/4 mile runs, you just have to level it, which is really easy.
It only works off of G force and time in this mode. So weight, wind,gear ratios, stuff like that DO NOT MATTER. It starts computing the moment the car moves. Go to the Gtech site, they video tape a run at the strip and times are the same
Again, I use it on my 2006 Gt mustang with Granatelli cold air intake all the time and run 0-60= 5.1 and 1/4 mile at 13.43 , which is right on the money for what the car should run. I really doubt anyone would argue that.
I ran the truck the first week I had it and ran 0-60=8.18 and 1/4 mile at 16.21. Right in line with Motortrend.
The track opens in few weeks and I will video tape my run with Gtech on dash