aftermaket tach tend to be more accurate, mainly because of the hook up point. I tap mine directly into distributor cap.. and the OEM tach is off by like 100rpm and get about 200rpm off by redline. Also for races, it is great to have one with a shift light, personal expericece in del sol. So piss when i bouced in 3rd.. had him by 1 1/2 car too. Well I do have to say that I have mine for looks, they are indiglo and matches my other guages.