Jon,
The gizmo for getting the odometer to read right is simply a signal generator, hooked to a small electric motor. The leads are connected to the new speedo, and the number of pulses it provides at the spinning speed is programmed into the speedo so it reads 84 mph while running. Obviously the speedo is also connected to a battery. Then you wait. Wait some more, wait even longer. Depends on how many miles you need to add. basically 84 mph is about 2000 miles in a 24 hour period. I need to rack up 143,000 miles so it is about 2 months. Today it reads 18,000 or so. I am patient.

Ans there are no mechanical parts in the new speedo, so there is no wear happening.