The speedometer needle is attached to a steel cup with a magnet spinning inside it, counterbalanced by a spring. There is no direct mechanical connection. The odometer gets its mileage reference from a direct gear drive, and is calibrated to show one mile (or a 1/10 fraction) every time the cable turns a set number of times. It's possible for the magnet/spring relationship to be off while the odometer is accurate, but that's pretty rare. Usually they're both off if the cable speed is incorrect.
Jerry
