328 speedometer reads high?

I just confirmed what I thought was the case: that my 328's speedometer is reading high... The one data point I have is at 40mph it reads 48. I'm not sure at this point if this is a fixed amount at all speeds (8mph), proportional to the speed (e.g., 20% higher), or some more complex function.

My mechanic swapped out the speedometer generating unit (speedo sender) (I have the old part) but the behavior with the new sender is identical.

A few questions. First, does the higher speed mean miles will accumulate faster? (I have yet to verify whether or not this is the case.) Is the device that turns the trip odometer and odometer separate from the speed generator itself?

Second, does the speedo just need to be recalibrated, or is it "fatally" flawed? If it needs recalibration, I may take it to a well-known shop here in Albuquerque called "Mo Ma" to check their capabilities / business practice.

Ferrari of UK, you wouldn't happen to have any specials on Speedos?


Take care,

--Mike