About a year ago both of my tachometers started misbehaving. Cruising at 1600 RPM the tachs would suddenly drop to 1100 RPM, then jump back up again. At times they would stay at the lower reading for an extended time. At other times they would function normally for days, weeks, or months. They have now been reading low for about one week. The reduction appears to be proportional to the RPM. Whereas tachometers are calibrated to the number of poles on the alternator, I'm wondering if my tachometers are telling me that I have a problem with my alternator. The alternator appears to be charging normally. Thanks for any guidance. Richard Allen "Sunshine Girl" 42 Bristol LRC Now on the hard at Safe Cove Boat Storage, Port Charlotte