chikin pickle

I just finished repairing my speedometer. However I removed the odometer from my car and placed it with the new speedometer that I removed from a junked accord I used the old odometer, with the new electric motor and printed circuit board. Now my speedometer appears to be roughly 5 mph fast based on the gear I'm using and the engine RPMs. (Its a manual trans)

So I'm curious as to the cause of this. I don't see how placing the needle in the wrong place could affect it as it would make sense that it would reset itself. I also placed it on the way it was when I took it off.

Could it be that the printed circuit board was out of a car that was factory equipped with larger rims/tires. (I swapped out the speedo control board) So that the circuit driving the guage is basing the reading off my tires which are smaller that the size it is programmed for? (195/50/R15)?

Which circuit is calibrated for tire size? The VSS itself, the speedo control board, or is it calibrated by the gear connected to the output shaft of the trans?