they are pretty accurate on the 1/4 mile times but are way off on the mph because in a real track the mph is averaged over the last (insert figure here... cause i dont rem i think its like 60ft)... and in the GTECH its "snapped" at exactly the end of the 1/4 so its always higher than you will get. My friends GT (houstongt) ran a 14.4 @ 103 on the gtech.. and 14.2 @ 98.8 at the track. So id say its fairly accurate except for the mph.