On the F355 tachometer there is a knob similar to the trip odometer reset knob located in the speedometer. The knob in the tachometer appears to be functionless to me. Does anyone know what this knob does or why it's there? (At least my 1999 F355 GTB has this on it's tachometer. I don't know if all F355s have this knob.) I can't find anything in the owner's manual referencing that knob.