Tony,
Another thing that the gauge manufactures don't tell you;
the needle movement is dampened so that the tach doesn't bounce all over the place.
This makes the tach slow to react to fast- going through the gears acceleration. I run a msd shift light with plug in pills. My 5" autometer tach is 400 rpm slow at 5,500 rpm .....The light comes on but the tach movement is only at 5 grand, so you are actually over revving your engine waiting for the tach to catch up.At a steady rate the tach is accurate.
Perry.
