The calibration of the ODO is in connection to the circuit board for the gage cluster.
The ODO doesnt get removed from the circuit board, and it retains the mileage of the car.
In order to keep the ODO legit, you remove the guages you want out of your second cluster and imput them into your original cluster with the original ODO, so ecentally you got New guage faces & the same old ODO.
NEVER take off the needles, unless your looking for trouble. Remove the guage unit as a whole (Speedo, tack, temp & gas guage) they come out EXTREAMLY easy.