I can answer my question due to curiousity. If you move your tach needle on accident downwards past the "0", the tach is then set at that position as zero rpms. To simply fix this you must turn the tach needle counterclockwise and stop the needle exactly on the "0" mark. What I kept doing was moving it clockwise to "0" which doesn't recalibrate it. Hope this helps people with the same problem...