It doesnt really matter to you unless your in a country that uses km/h. If your in the states you will be switching a mph cluster for a km/h so your mileage will be wrong no matter what, most people want to get either the lowest mileage possible to sell it for more in the car or get the closest matching odometer to their true mileage. What some people dont know is its very easy to roll these odometers to either lie about mileage or put a new cluster in with exact matching mileage as before.
1 mile =1.609 344 kilometers. Im not sure if it works this way (idk if the gearing difference is in the cluster or vss) but you could probably roll it to your mileage and start acting like its miles on the odometer rather than kilometers