It does not use GPS ... it works on Gen 1 and 2 iPhones and also the iTouch ... it uses the accelerometer and nothing else ...

Here is a review ... it is very accurate ...

http://www.youtube.com/watch?v=0-DFbJQbeSY


"Here are some tips for getting the best accuracy out of Dynolicious:

First, make sure you have the iPhone mounted correctly. It is critical that the iPhone is facing the front of the vehicle. It can be angled up or down, but not side to side. See the images in the "manual" section of the setup screen if this is not clear.
Run the calibration from the setup menu. This compensates for inaccuracies in your iPhone's accelerometer. (If you are one of the people who's phone will not calibrate, make sure you update to Dynolicious v1.1)

Make sure that your test surface is fairly level. If you start or end facing uphill or downhill, this will significantly affect your numbers.

If your aim is to measure HP, try not to jerk the car at takeoff. A smooth acceleration at takeoff and then wide open throttle will generate the most consistent results. (v1.1 should be more resiliant against rough takeoffs and provide better HP results.)

Make sure that the weight specified includes all passengers, cargo, accessories, etc.

Make sure the iPhone is mounted so that it cannot move relative to the car. Cradles that bounce while driving have a serious effect on accuracy.

If you believe you are getting false triggering, meaning that the timer starts before you start accelerating, please increase the trigger value in the settings.
Hope this helps,
Justin
BunsenTech, LLC "

 

I had read about it using the accelerometer. Also did some searching on GPS and it can be off as much as 50 feet which would make it a pretty poor tool here. I wondered if it worked on the ipod touch.

 

I just ordered this off of Amazon as well, thanks for the review.

 

You're welcome!