I consistently ran my G-Tech Pro against the drag strip timers for comparisons on at least 20 - 25 runs. I found the accuracy a bit hit and miss, sometimes it was within 0.01sec, other times it was out by almost 1 sec.

The G-Tech pro is handy for analysing your runs afterwards. Using the plot feature, you can work out where you lost traction, at what rev you changed gear, how quickly you changed while maintaining power etc. That's handy for working out the ideal rpm for changing gears, eg if you can hold 160kmh in 3rd, you may be better off not changing into 4th.