Hi All new to the group !!!!! Help 1990 Tach reading too high

Just bought my first Corvette after many years of waiting !!!!!! I have a 1990 red convertable 6 spd and just love it. One thing I noticed that
the tach is reading high about twice what it should the reading is not erratic I have checked rpm with another tach and the actual engine rpms are good. Anybody know the fix????? Thanks TB
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