Discrepancy between tach and data loger

Their is a 1500 rpm discrepancy between my Autometer memory tach and my RPM data logger. With the tach being the higher. I have a mag 44 so the tach signal is going through a MSD Pro Mag Converter. Any one ever have this problem?

 

You don't say how long you have had the tach. I would discuss this directly with Autometer. Tire shake with funny cars will kill these easily. If you talk to the tech people they will fill the circuit board to stop cracks and pieces falling off. You won't find this mentioned anywhere. My experience is it goes wonky when something happens to the board. I would also go to the MSD website (http://www.msdpromag.com/) and download the correct schematic just to make sure it is wired properly.
Hope this helps
Dale

 

The tach has about two dozen runs on it. A couple of witch it shook pretty hard.