How does one know if there tach is correct? I have an after market tach in my car and the highest it has read was 8600. my stock tach was broken for the longest time, (brake in the wire behind cluster) and when it says 5 my aftermarket one says 3.5. Meaning my engine reved to like 11000, but i have the stock nikki carb and fuel pump. so now i need to know what the hell is up.