One day after spotting the "inexpensive" auto performance measurement tool Dynolicious for the iPhone, we've found another, and it's much cheaper. Liberty For One has released its own automotive measurement tool called g-tac, and its going for just $4.99. For less than half the cost of the Dynolicious tool, you get times and trap speed for the quarter mile, as well as times for 0-60 and 60-0. The g-tac utilizes the iPhone's (and iPod Touch's) accelerometer to determine velocity, so the phone doesn't have to be plugged into the car. The tool also graphs out your last three runs so you can hone your launch technique over time.